The COVID-19 pandemic has had a devastating impact on the world over the past two years (2020-2021). One of the key questions about its future trajectory is the protection from subsequent infections and disease conferred by a previous infection, as the SARS-CoV-2 virus belongs to the coronaviruses, a group of viruses the members of which are known for their ability to reinfect convalescent individuals. Bulgaria, with high rates of previous infections combined with low vaccination rates and an elderly population, presents a somewhat unique context to study this question.
We use detailed governmental data on registered COVID-19 cases to evaluate the incidence and outcomes of COVID-19 reinfections in Bulgaria in the period between March 2020 and early December 2021.
For the period analyzed, a total of 4,106 cases of individuals infected more than once were observed, including 31 cases of three infections and one of four infections. The number of reinfections increased dramatically during the Delta variant-driven wave of the pandemic towards the end of 2021. We observe a moderate reduction of severe outcomes (hospitalization and death) in reinfections relative to primary infections, and a more substantial reduction of severe outcomes in breakthrough infections in vaccinated individuals.
Citation: Marinov GK, Mladenov M, Rangachev A, Alexiev I (2022) SARS-CoV-2 reinfections during the first three major COVID-19 waves in Bulgaria. PLoS ONE 17(9): e0274509. https://doi.org/10.1371/journal.pone.0274509
Editor: Debdutta Bhattacharya, Regional Medical Research Centre Bhubaneswar, INDIA
Received: March 24, 2022; Accepted: August 30, 2022; Published: September 9, 2022
Copyright: © 2022 Marinov et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All datasets and associated code can be found at https://github.com/Mlad-en/Cov-Reinfections.
Funding: The author(s) received no specific funding for this work.
Competing interests: The authors have declared that no competing interests exist.
The COVID-19 [1–3] pandemic has become the most significant public health crisis in more than a century, and is still rapidly developing. An important question for its future trajectory, especially given the large and steadily growing number of infected individuals in most countries, is the degree of protection from subsequent infection and serious disease that prior SARS-CoV-2 infection and recovery confers.
SARS-CoV-2 belongs to the coronavirus family, of which four different endemic human viruses were known prior to the pandemic—HCoV-OC43 [4, 5], HCoV-229E , HCoV-NL63 [7, 8] and HCoV-HKU1 [9–11]. These usually cause common colds (around 10-15% of colds, depending on the source [12–15], are considered to be caused by them), and, as is common with respiratory viruses , they cause repeated reinfections throughout people’s lifetimes . Large coronavirus epidemics are thought to occur at two- to three-year intervals [18, 19], though these are generally not noticed by society due to the overall mild nature of these viruses.
Given that SARS-CoV-2 belongs to the same family of viruses, it is natural to expect that a similar host-pathogen dynamics involving frequent reinfections will be observed with it too.
The first reports of repeated infections appeared very early in the pandemic . However, at the time it was difficult to exclude the possibility of simple persistence of viral RNA as opposed to true reinfections. Viral genomic sequencing (showing that distinct viral lineages infected the same individual more than once) eventually proved beyond reasonable doubt that reinfection occurs, but it was still initially seen as an exotic and surprising phenomenon [21–27]. Since then, however, reinfection has been proven to be far from a rare phenomenon as a large body of case reports has accumulated from around the world [28–121], most recently including even cases of third infections [38, 122, 123].
A number of cohort studies have also been published [123–173], but most of these suffer from various drawbacks, such as the inclusion of a very narrow time window after initial infection, focus on healthcare workers (meaning that the age distribution is not representative of the overall population), and the fact that most such studies were carried out prior to the appearance of the more highly derived SARS-CoV-2 variants that have come to dominate the pandemic in 2021 and 2022. The importance of comprehensive population sampling was shown by a recent reinfection study from Denmark , which found protection from reinfection of only 47.1% among those 65 years old and older during the late-2020 surge as opposed to 80.5% for the general population. The importance of variants was first stressed by the placebo arm of the clinical trial of the Novavax vaccine in South Africa , which showed little protection of prior infection against infection with the dominant at the time there B.1.351 variant .
Later, towards the end of 2021, the Omicron lineage of variants emerged, with very strong immune escape characteristics [176–179] and the ability to reinfect convalescent individuals at a high rate [123, 180–183].
In this work, we analyze available reinfection data in Bulgaria prior to the emergence of the Omicron variant, when largely homologous antigenically variants were circulating. Bulgaria has been one of the most seriously affected by the pandemic countries , having experienced three major COVID-19 waves in 2020-2021 and exhibiting excess mortality approaching 1% of its population within that period . In the same time, only a small portion of the population has been fully vaccinated (≤30% by the end of 2021), meaning that the country provides a unique context in which the clinical impact of reinfections can be observed in a previously severely impacted population with an age structure skewed towards the elderly individuals, but without the confounding factor of high vaccination coverage. We identify 4,106 reinfected individuals out of ≤700,000 cases in the country prior to December 2021. The frequency of reinfection increased substantially during the third wave driven by the Delta variant, at which point reinfections represented ∼2.2% of cases, with protection conferred by previous infection ∼81%. The severity of reinfections (i.e. the rate of hospitalizations and fatalities) was comparable to that of primary infections, while severity was reduced in breakthrough infections in vaccinated uninfected subjects.
The research described in this manuscript has been approved by the Ethics Committee of the IMI-BAS (Institute of Mathematics and Informatics, Bulgarian Academy of Sciences).
Primary SARS-CoV-2 Infections in Bulgaria.
At the time of writing this manuscript, there were no publicly available age-stratified datasets on hospitalizations and deaths associated with confirmed SARS-CoV-2 infections in Bulgaria. We obtained a patient-sensitive dataset from Bulgaria’s Ministry of Health, which included data on all infections from the beginning of the pandemic until November 5th 2021.
This dataset included information about a person’s age, gender, region, the date of their latest Covid-19 test, their status (infected, recovered, hospitalized, deceased), their hospitalization start and end dates, if any, information about accompanying diseases, as well as whether they received any breathing assistance, whether they were taken into intensive care and whether they died of Covid-19.
Data on breakthrough infections in vaccinated individuals.
Information about infections, hospitalizations and deaths among the vaccinated population in Bulgaria were obtained through publicly available datasets provided by Bulgaria’s Ministry of Health. These datasets present a daily time series that contain information about the age at 10 year intervals, gender, vaccination course and count of infected, hospitalized or deceased per group.
No publicly available datasets about the reinfection rates in Bulgaria existed prior to the writing of this manuscript. We obtained these datasets through a separate request for information on patient-sensitive data from Bulgaria’s Ministry of Health. The data provided by the Ministry covers the period from the beginning of the pandemic until December 9th 2021.
Reinfections were defined as cases of two positive tests spaced ≥90 days apart.
Breakthrough reinfections were defined as cases of a second positive tests at least one day after the completion of the vaccination course.
SARS-CoV-2 sequencing data.
Information about sequenced SARS-CoV-2 genomes was obtained from the GISAID database .
Suspected SARS-CoV-2 reinfection cases in Bulgaria
In order to identify SARS-CoV-2 reinfection cases in Bulgaria, we obtained datasets on the incidence and clinical outcomes of suspected reinfections up to December 9th 2021. We classified cases as suspected reinfections if ≥90 days have passed between testing positive on at least two different occasions.
After largely successfully escaping the first global wave of infections in the first half of 2020, Bulgaria experienced three major waves of COVID-19, in October-December 2020, in February-April 2021, and in the later months of 2021, of roughly equal magnitude (Fig 1A). Under this criterion, the eligible population to be considered for potential reinfection was ∼200,000 individuals after the first major wave, doubling to ≥400,000 after the second (Fig 1B). These waves were driven by different variants of the SARS-CoV-2 virus. The first was dominated by B.1 lineages antigenically similar to the ancestral strain. The second consisted almost entirely of the Alpha (B.1.1.7) variant [187, 188], while in the third the globally dominant by then Delta (B.184.108.40.206/AY.*) variant  constituted practically all cases (Fig 1C). We have defined for the purposes of our analyses the dividing lines between these waves as mid-January 2021 and beginning of June 2021.
(A) Primary infections in Bulgaria over time. Bulgaria has so far experienced three distinct major epidemiological waves of COVID-19, with peaks in November 2020, March 2021, and October 2021 (an initial wave did occur in the first half of 2020 but it was very small and generally successfully suppressed, and is of little relevance to the progression of the pandemic in the country). (B) Number of people eligible to be considered for reinfection, i.e. people who have tested positive and ≥90 days have elapsed since that positive test. (C) Dominant variants in Bulgaria over time. The first major wave was driven by early B.1/B.1.* derivative variants. The second wave was associated with the Alpha/B.1.1.7 variant. The third wave was dominated by the Delta/B.1.617.2 variant and its AY.* sublineages. (D) Number of probable reinfections over time in Bulgaria (per week).
In total, we identified 4,106 cases of individuals infected more than once, including 31 cases of people infected three times and one case of a quadruple infection.
The number of reinfections in the first major wave in late 2020 was small, peaking at ≤100 such cases weekly, reflecting the low incidence of COVID-19 earlier that year (Fig 1C). A larger, though still relatively small number of reinfections were observed during the Alpha wave in the first half of 2021. The bulk of reinfections came during the Delta wave in the second half of the year, peaking at 755 a week at the end of October 2021. During the Delta wave reinfections constituted ∼2.3% of cases in Bulgaria. Taking into account the number of eligible for reinfection individuals, during the months of October and November protection from reinfection is estimated to have stood at ∼81% (95% CI , 63% to 100%).
We then examined the time between primary and subsequent infections. We observe a peak at approximately a year from the initial infection, but the distribution is highly dispersed and a large number of reinfections are observed all throughout the interval from 90 to 360 days (Fig 2A). These numbers correspond primarily to a cohort of people who were infected in the first wave and then reinfected in the Delta wave (n = 1, 674), and another group of people infected during the Alpha wave and then reinfected during the Delta wave (n = 1, 435).
(A) Distribution of the length of the interval between primary infection and reinfection. (B) Primary infections and reinfections by wave and dominant variant. Waves were defined as follows: “initial infections” refers to the period prior to September 2020; “1st wave” refers to the period between September 2020 and the middle of January 2020, during which D614G variants without many other notable mutations were dominant; the “2nd wave”, between mid-January 2021 and June 2021 was dominated by the B.1.1.7/Alpha variant; the “3rd wave”, dominated by the B.1.617.2/Delta variant, began in July 2021.
Clinical severity of reinfections
We then analyzed the clinical outcomes of reinfections and compared it to outcomes from primary infections and from infections in vaccinated individuals (“breakthrough infections”).
Among the 4,106 reinfections, 413 were also “breakthrough reinfections”, i.e. the reinfection occurred after a vaccination course was completed. We divided the reinfection cases into separate unvaccinated and breakthrough reinfection categories.
A total of 84 fatalities were recorded within the reinfected cases, one of them within the set of 31 individuals with three infections. This corresponds to an apparent lower case fatality rate (CFR) than the total CFR in Bulgaria for the studied period (∼2% compared to ∼4.2%). In terms of hospitalizations, for the 4,106 reinfected individuals, 705 hospitalizations were recorded for the second infections (a rate of 17.7%); this compares to 8,177 hospitalizations out of 49,170 breakthrough cases in vaccinated individuals (16.6%) and 109,108 hospitalizations out of 332,510 total primary infections (32.8%). However, such comparisons based on total numbers are confounded by the fact that populations are not age matched.
We therefore divided cases in all four categories into age groups and compared the rates of hospitalizations and fatalities in each (Fig 3). This analysis reveals a moderately reduced rate of hospitalizations between primary infections and reinfections across all age groups (we observe 40% reduction of risk in the 20-60 age group and 31% in the 60+ age group for the unvaccinated reinfected, and 60% and 40% for the vaccinated reinfected, respectively), and a less pronounced risk of death (38% reduction in the 20-60 age group and 25% in the 60+ age group for the unvaccinated reinfected; note that total numbers were too small for breakthrough reinfections for an accurate estimate). For comparison the severity of breakthrough infections was more strongly reduced compared to primary infections in the unvaccinated (60%/70% risk reductions for hospitalization/death in the 20-60 age group and 49%/66% in the 60+), although that effect diminished in the higher age groups (consistent with previous findings of lower vaccine efficacy in the elderly [191–193]).
(A) Percentage of hospitalizations among cases in primary infections, breakthrough infections (infections in vaccinated individuals), reinfections (divided into reinfections in the unvaccinated and breakthrough reinfections); (B) Percentage of deaths among cases in primary infections, breakthrough infections (infections in vaccinated individuals), reinfections (divided into reinfections in the unvaccinated and breakthrough reinfections). Binomial proportion confidence intervals were estimated using the Clopper-Pearson exact binomial interval method. (C) Age distribution of reinfected individuals.
In this study we evaluated the rate of incidence and the clinical outcomes of SARS-CoV-2 reinfections during the first three waves of the COVID-19 pandemic in Bugaria, and compared them to primary infections and breakthrough infections in vaccinated individuals. The bulk of reinfections happened during the Delta variant-driven wave, with prior infection providing protection from reinfection at ∼80%. Clinical severity was somewhat reduced relative to primary infections, but to a lesser extent than the observed reduction in severity in breakthrough infections in the vaccinated. A possible limitation of our study is the possibility that in some individuals the disease may have passed with mild symptoms or asymptomatically, and thus not all cases have been properly diagnosed and registered in the national system, leading to some bias towards documenting symptomatic infections. Results regarding the relative severity of reinfections in the literature have ranged from finding no difference in the severity of reinfections and primary infection to finding considerable (though rarely very high) degree of reduction from severe outcomes ; our results also fit within this range of estimates.
The authors would like to acknowledge the help of the Bulgarian Ministry of Health and Information Services for providing us with raw data about reinfections, demographics and vaccination status.
- 1. Wang C, Horby PW, Hayden FG, Gao GF. 2020. A novel coronavirus outbreak of global health concern. Lancet 395(10223):470–473. pmid:31986257
- 2. Zhou P, Yang XL, Wang XG, Hu B, Zhang L, Zhang W, et al. 2020. A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature 579(7798):270–273. pmid:32015507
- 3. Huang C, Wang Y, Li X, Ren L, Zhao J, Hu Y, et al. 2020. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet 395(10223):497–506. pmid:31986264
- 4. McIntosh K, Becker WB, Chanock RM. 1967. Growth in suckling-mouse brain of “IBV-like” viruses from patients with upper respiratory tract disease. Proc Natl Acad Sci U S A 58(6):2268–2273 pmid:4298953
- 5. McIntosh K, Dees JH, Becker WB, Kapikian AZ, Chanock RM. 1967. Recovery in tracheal organ cultures of novel viruses from patients with respiratory disease. Proc Natl Acad Sci USA 57:933–940. pmid:5231356
- 6. Hamre D, Procknow JJ. 1966. A new virus isolated from the human respiratory tract. Proc Soc Exp Biol Med 121(1):190–193 pmid:4285768
- 7. Fouchier RA, Hartwig NG, Bestebroer TM, Niemeyer B, de Jong JC, Simon JH, et al. 2004. A previously undescribed coronavirus associated with respiratory disease in humans. Proc Natl Acad Sci U S A 101(16):6212–6216 pmid:15073334
- 8. Pyrc K, Jebbink MF, Berkhout B, van der Hoek L. 2004. Genome structure and transcriptional regulation of human coronavirus NL63. Virol J 1:7 pmid:15548333
- 9. Woo PC, Lau SK, Chu CM, Chan KH, Tsoi HW, Huang Y, et al. 2005. Characterization and complete genome sequence of a novel coronavirus, coronavirus HKU1, from patients with pneumonia. J Virol 79(2):884–895 pmid:15613317
- 10. Lau SK, Woo PC, Yip CC, Tse H, Tsoi HW, Cheng VC, et al. 2006. Coronavirus HKU1 and other coronavirus infections in Hong Kong. J Clin Microbiol 44(6):2063–2071 pmid:16757599
- 11. Vabret A, Dina J, Gouarin S, Petitjean J, Corbet S, Freymuth F. 2006. Detection of the new human coronavirus HKU1: a report of 6 cases. Clin Infect Dis 42(5):634–639 pmid:16447108
- 12. Wat D. 2004. The common cold: a review of the literature. Eur J Intern Med 15(2):79–88
- 13. Mäkelä MJ, Puhakka T, Ruuskanen O, Leinonen M, Saikku P, Kimpimäki M, et al. 1998. Viruses and bacteria in the etiology of the common cold. J Clin Microbiol 36(2):539–542. pmid:9466772
- 14. Larson HE, Reed SE, Tyrrell DA. 1980. Isolation of rhinoviruses and coronaviruses from 38 colds in adults. J Med Virol 5(3):221–29 pmid:6262450
- 15. Nicholson KG, Kent J, Hammersley V, Cancio E. 1997. Acute viral infections of upper respiratory tract in elderly people living in the community: comparative, prospective, population based study of disease burden. BMJ 315(7115):1060–1064 pmid:9366736
- 16. Yewdell JW. 2021. Individuals cannot rely on COVID-19 herd immunity: Durable immunity to viral disease is limited to viruses with obligate viremic spread. PLoS Pathog 17(4):e100950
- 17. Callow KA, Parry HF, Sergeant M, Tyrrell DA. 1990. The time course of the immune response to experimental coronavirus infection of man. Epidemiol Infect 105:435–446. pmid:2170159
- 18. Monto AS. Medical reviews: coronaviruses. Yale J Biol Med 47:234–251. pmid:4617423
- 19. Kahn JS, McIntosh K. 2005. History and recent advances in coronavirus discovery. Pediatr Infect Dis J 24(11 Suppl):S223–227. pmid:16378050
- 20. Mahase E. 2020. Covid-19: WHO and South Korea investigate reconfirmed cases. BMJ 369:m1498
- 21. de Vrieze J. 2020. Reinfections, still rare, provide clues on immunity. Science 370(6519):895–897. pmid:33214256
- 22. Arafkas M, Khosrawipour T, Kocbach P, Zielinski K, Schubert J, Mikolajczyk A, et al. 2021. Current meta-analysis does not support the possibility of COVID-19 reinfections. J Med Virol 93(3):1599–1604. pmid:32897549
- 23. Ledford H. 2020. Coronavirus reinfections: three questions scientists are asking. Nature 585(7824):168–169. pmid:32887957
- 24. Jabbari P, Rezaei N. 2020. With Risk of Reinfection, Is COVID-19 Here to Stay? Disaster Med Public Health Prep 14(4):e33 pmid:32713383
- 25. Duggan NM, Ludy SM, Shannon BC, Reisner AT, Wilcox SR. 2021. Is novel coronavirus 2019 reinfection possible? Interpreting dynamic SARS-CoV-2 test results. Am J Emerg Med 39:256.e1–256.e3. pmid:32703607
- 26. York A. 2020. Can COVID-19 strike twice? Nat Rev Microbiol 18(9):477. pmid:32690876
- 27. Law SK, Leung AWN, Xu C. 2020. Is reinfection possible after recovery from COVID-19? Hong Kong Med J 26(3):264–265. pmid:32536614
- 28. Tang CY, Wang Y, McElroy JA, Li T, Hammer R, Ritter D, et al. 2021. Reinfection with two genetically distinct SARS-CoV-2 viruses within 19 days. J Med Virol 93(10):5700–5703. pmid:34170528
- 29. Lee JS, Kim SY, Kim TS, Hong KH, Ryoo NH, Lee J, et al. 2020. Evidence of Severe Acute Respiratory Syndrome Coronavirus 2 Reinfection After Recovery from Mild Coronavirus Disease 2019. Clin Infect Dis ciaa1421.
- 30. Mulder M, van der Vegt DSJM, Oude Munnink BB, GeurtsvanKessel CH, van de Bovenkamp J, Sikkema RS, et al. 2020. Reinfection of SARS-CoV-2 in an immunocompromised patient: a case report. Clin Infect Dis ciaa1538
- 31. To KK, Hung IF, Ip JD, Chu AW, Chan WM, Tam AR, et al. 2020. COVID-19 re-infection by a phylogenetically distinct SARS-coronavirus-2 strain confirmed by whole genome sequencing. Clin Infect Dis ciaa1275
- 32. Larson D, Brodniak SL, Voegtly LJ, Cer RZ, Glang LA, Malagon FJ, et al. 2020. A Case of Early Re-infection with SARS-CoV-2. Clin Infect Dis ciaa1436
- 33. Goldman JD, Wang K, Roltgen K, Nielsen SCA, Roach JC, Naccache SN, et al. 2020. Reinfection with SARS-CoV-2 and Failure of Humoral Immunity: a case report. medRxiv 2020.09.22.20192443 pmid:32995830
- 34. Tillett RL, Sevinsky JR, Hartley PD, Kerwin H, Crawford N, Gorzalski A, et al. 2021. Genomic evidence for reinfection with SARS-CoV-2: a case study. Lancet Infect Dis 21(1):52–58. pmid:33058797
- 35. Prado-Vivar B, Becerra-Wong M, Guadalupe JJ, Márquez S, Gutierrez B, Rojas-Silva P, et al. 2021. A case of SARS-CoV-2 reinfection in Ecuador. Lancet Infect Dis 21(6):e142. pmid:33242475
- 36. Sevillano G, Ortega-Paredes D, Loaiza K, Zurita-Salinas C, Zurita J. 2021. Evidence of SARS-CoV-2 reinfection within the same clade in Ecuador: A case study. Int J Infect Dis 108:53–56. pmid:33930542
- 37. Gupta V, Bhoyar RC, Jain A, Srivastava S, Upadhayay R, Imran M, et al. 2020. Asymptomatic reinfection in two healthcare workers from India with genetically distinct SARS-CoV-2. Clin Infect Dis ciaa1451
- 38. Shastri J, Parikh S, Agrawal S, Chatterjee N, Pathak M, Chaudhary S, et al. 2021. Clinical, Serological, Whole Genome Sequence Analyses to Confirm SARS-CoV-2 Reinfection in Patients From Mumbai, India. Front Med (Lausanne) 8:631769 pmid:33768104
- 39. Resende PC, Bezerra JF, Teixeira Vasconcelos RH, Arantes I, Appolinario L, MendonÃ§a AC, et al. 2021. Severe Acute Respiratory Syndrome Coronavirus 2 P.2 Lineage Associated with Reinfection Case, Brazil, June-October 2020. Emerg Infect Dis 27(7):1789–1794. pmid:33883059
- 40. Nonaka CKV, Franco MM, Gräf T, de Lorenzo Barcia CA, de Ávila Mendonca RN, de Sousa KAF, et al. 2021. Genomic Evidence of SARS-CoV-2 Reinfection Involving E484K Spike Mutation, Brazil. Emerg Infect Dis 27(5):1522–1524. pmid:33605869
- 41. Mahajan NN, Gajbhiye RK, Lokhande PD, Bahirat S, Modi D, Mathe AM, et al. 2021. Clinical Presentation of Cases with SARS-CoV-2 Reinfection/ Reactivation. J Assoc Physicians India 69(1):16–18. pmid:34227769
- 42. Garvey MI, Casey AL, Wilkinson MAC, Ratcliffe L, McMurray C, Stockton J, et al. 2021. Details of SARS-CoV-2 reinfections at a major UK tertiary centre. J Infect 82(6):e29–e30. pmid:33744302
- 43. Harrington D, Kele B, Pereira S, Couto-Parada X, Riddell A, Forbes S, et al. 2021. Confirmed Reinfection with SARS-CoV-2 Variant VOC-202012/01. Clin Infect Dis ciab014 pmid:33421056
- 44. Zucman N, Uhel F, Descamps D, Roux D, Ricard JD. 2021. Severe reinfection with South African SARS-CoV-2 variant 501Y.V2: A case report. Clin Infect Dis ciab129
- 45. Ramírez JD, Muñoz M, Ballesteros N, Patiño LH, Castañeda S, Rincón CA, et al. 2021. Phylogenomic Evidence of Reinfection and Persistence of SARS-CoV-2: First Report from Colombia. Vaccines (Basel) 9(3):282. pmid:33808687
- 46. Van Elslande J, Vermeersch P, Vandervoort K, Wawina-Bokalanga T, Vanmechelen B, Wollants E, et al. 2021. Symptomatic Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Reinfection by a Phylogenetically Distinct Strain. Clin Infect Dis 73(2):354–356. pmid:32887979
- 47. Tomassini S, Kotecha D, Bird PW, Folwell A, Biju S, Tang JW. 2021. Setting the criteria for SARS-CoV-2 reinfection—six possible cases. J Infect 82(2):282–327. pmid:32800801
- 48. Hoang VT, Dao TL, Gautret P. 2020. Recurrence of positive SARS-CoV-2 in patients recovered from COVID-19. J Med Virol 92(11):2366–2367. pmid:32449789
- 49. Bongiovanni M. 2021. COVID-19 reinfection in a healthcare worker. J Med Virol 93(7):4058–4059. pmid:32990954
- 50. Salzer HJF, Neuböck M, Heldt S, Haug I, Paar C, Lamprecht B. 2021. Emerging COVID-19 reinfection four months after primary SARS-CoV-2 infection. Wien Med Wochenschr 1–3. pmid:33555412
- 51. Sicsic I Jr, Chacon AR, Zaw M, Ascher K, Abreu A, Chediak A. 2021. A case of SARS-CoV-2 reinfection in a patient with obstructive sleep apnea managed with telemedicine. BMJ Case Rep 14(2):e240496
- 52. Salcin S, Fontem F. 2021. Recurrent SARS-CoV-2 infection resulting in acute respiratory distress syndrome and development of pulmonary hypertension: A case report. Respir Med Case Rep 33:101314. pmid:33312856
- 53. Selhorst P, Van Ierssel S, Michiels J, Maria J, Bartholomeeusen K, Dirinck E, et al. 2020. Symptomatic SARS-CoV-2 reinfection of a health care worker in a Belgian nosocomial outbreak despite primary neutralizing antibody response. Clin Infect Dis ciaa1850.
- 54. Scarpati G, Piazza O, Pagliano P, Rizzo F. 2021. COVID-19: a confirmed case of reinfection in a nurse. BMJ Case Rep 14(7):e244507 pmid:34257135
- 55. Garg J, Agarwal J, Das A, Sen M. 2021. Recurrent COVID-19 infection in a health care worker: a case report. J Med Case Rep 15(1):363 pmid:34253225
- 56. Goes LR, Siqueira JD, Garrido MM, Alves BM, Pereira ACPM, Cicala C, et al. 2021. New infections by SARS-CoV-2 variants of concern after natural infections and post-vaccination in Rio de Janeiro, Brazil. Infect Genet Evol 94:104998 pmid:34252616
- 57. Ahmadian S, Fathizadeh H, Shabestari Khiabani S, Asgharzadeh M, Kafil HS. 2021. COVID-19 reinfection in a healthcare worker after exposure with high dose of virus: A case report. Clin Case Rep 9(6):e04257. pmid:34194783
- 58. Amorim MR, Souza WM, Barros ACG Jr, Toledo-Teixeira DA, Dos-Santos KB, Simeoni CL, et al. 2021. Respiratory Viral Shedding in Healthcare Workers Reinfected with SARS-CoV-2, Brazil, 2020. Emerg Infect Dis 27(6):1737–1740. pmid:33871331
- 59. Bongiovanni M, Marra AM, Bini F, Bodini BD, Carlo DD, Giuliani G. 2021. COVID-19 reinfection in healthcare workers: A case series. J Infect 82(6):e4–e5. pmid:33839184
- 60. Salehi-Vaziri M, Omrani MD, Pouriayevali MH, Fotouhi F, Banifazl M, Farahmand B, et al. 2021. SARS-CoV-2 presented moderately during two episodes of the infection with lack of antibody responses. Virus Res 299:198421. pmid:33836204
- 61. Bonifácio LP, Pereira APS, Araújo DCAE, Balbão VDMP, Fonseca BALD, Passos ADC, et al. 2020. Are SARS-CoV-2 reinfection and Covid-19 recurrence possible? a case report from Brazil. Rev Soc Bras Med Trop 53:e20200619 pmid:32965458
- 62. Silva MSD, Demoliner M, Hansen AW, Gularte JS, Silveira F, Heldt FH, et al. 2021. Early detection of SARS-CoV-2 P.1 variant in Southern Brazil and reinfection of the same patient by P.2. Rev Inst Med Trop Sao Paulo 63:e58 pmid:34231823
- 63. Yu ALF, Liphaus BL, Ferreira PM, Tanamachi AT, Masuda ET, Trevisan CM, et al. 2021. SARS-CoV-2 reinfection: report of two cases in Southeast Brazil. Rev Inst Med Trop Sao Paulo 63:e50. pmid:34161556
- 64. Romano CM, Felix AC, Paula AV, Jesus JG, Andrade PS, Cándido D, et al. 2021. SARS-CoV-2 reinfection caused by the P.1 lineage in Araraquara city, Sao Paulo State, Brazil. Rev Inst Med Trop Sao Paulo 63:e36. pmid:33909850
- 65. West J, Everden S, Nikitas N. 2021. A case of COVID-19 reinfection in the UK. Clin Med (Lond) 21(1):e52–e53. pmid:33303623
- 66. Sharma R, Sardar S, Mohammad Arshad A, Ata F, Zara S, Munir W. 2020. A Patient with Asymptomatic SARS-CoV-2 Infection Who Presented 86 Days Later with COVID-19 Pneumonia Possibly Due to Reinfection with SARS-CoV-2. Am J Case Rep 21:e927154 pmid:33257644
- 67. Ozaras R, Ozdogru I, Yilmaz AA. 2020. Coronavirus disease 2019 re-infection: first report from Turkey. New Microbes New Infect 38:100774. pmid:33235800
- 68. Colson P, Finaud M, Levy N, Lagier JC, Raoult D. 2021. Evidence of SARS-CoV-2 re-infection with a different genotype. J Infect 82(4):84–123. pmid:33207255
- 69. Selvaraj V, Herman K, Dapaah-Afriyie K. 2020. Severe, Symptomatic Reinfection in a Patient with COVID-19. R I Med J (2013) 103(10):24–26.
- 70. AlFehaidi A, Ahmad SA, Hamed E. 2021. SARS-CoV-2 re-infection: a case report from Qatar. J Infect 82(3):414–451. pmid:33115660
- 71. de Brito CAA, Lima PMA, de Brito MCM, de Oliveira DB. 2020. Second Episode of COVID-19 in Health Professionals: Report of Two Cases. Int Med Case Rep J 13:471–475
- 72. Hanif M, Haider MA, Ali MJ, Naz S, Sundas F. 2020. Reinfection of COVID-19 in Pakistan: A First Case Report. Cureus 12(10):e11176. pmid:33262913
- 73. Ferrante L, Livas S, Steinmetz WA, Almeida ACL, Leão J, Vassão RC, et al. 2021. The First Case of Immunity Loss and SARS-CoV-2 Reinfection by the Same Virus Lineage in Amazonia. J Racial Ethn Health Disparities 8(4):821–823 pmid:34155594
- 74. Arteaga-Livias K, Panduro-Correa V, Pinzas-Acosta K, Perez-Abad L, Pecho-Silva S, Espinoza-Sánchez F, et al. 2021. COVID-19 reinfection? A suspected case in a Peruvian patient. Travel Med Infect Dis 39:101947 pmid:33307196
- 75. Novoa W, Miller H, Mattar S, Faccini-Martínez A, Rivero R, Serrano-Coll H. 2021. A first probable case of SARS-CoV-2 reinfection in Colombia. Ann Clin Microbiol Antimicrob 20(1):7 pmid:33435982
- 76. Alzedam A, Bengblya AM, Zeglam MJ, Benmassoud ET, Bennji SM. 2021. A case of COVID-19 re-infection in Libya. Afr J Thorac Crit Care Med 27(2). pmid:34430866
- 77. Camargo CH, Goncalves CR, Pagnoca EVRG, Campos KR, Montanha JOM, Flores MNP, et al. SARS-CoV-2 reinfection in a healthcare professional in inner Sao Paulo during the first wave of COVID-19 in Brazil Diagn Microbiol Infect Dis. 101(4):115516
- 78. Díaz Y, Ortiz A, Weeden A, Castillo D, González C, Moreno B, et al. 2021. SARS-CoV-2 reinfection with a virus harboring mutation in the Spike and the Nucleocapsid proteins in Panama. Int J Infect Dis 108:588–591. pmid:34107326
- 79. Aguilar-Shea AL, Gutiérrez-Martín-Arroyo J, Vacas-Córdoba M, Gallardo-Mayo C. 2021. Reinfection by SARS-CoV-2: The first one in a family reported in Spain. Med Clin (Barc) S0025-7753(21)00250–5
- 80. Rodríguez-Espinosa D, Broseta Monzó JJ, Casals Q, Piñeiro GJ, Rodas L, Vera M, Maduell F. 2021. Fatal SARS-CoV-2 reinfection in an immunosuppressed patient on hemodialysis. J Nephrol 34(4):1041–1043. pmid:34097293
- 81. Sanyang B, Kanteh A, Usuf E, Nadjm B, Jarju S, Bah A, et al. 2021. COVID-19 reinfections in The Gambia by phylogenetically distinct SARS-CoV-2 variants-first two confirmed events in west Africa. Lancet Glob Health 9(7):e905–e907 pmid:34090610
- 82. Loconsole D, Sallustio A, Accogli M, Centrone F, Casulli D, Madaro A, et al. 2021. Symptomatic SARS-CoV-2 Reinfection in a Healthy Healthcare Worker in Italy Confirmed by Whole-Genome Sequencing. Viruses 13(5):899 pmid:34066205
- 83. Garduño-Orbe B, Sánchez-Rebolledo JM, Cortés-Rafael M, García-Jiménez Y, Perez-Ortiz M, Mendiola-Pastrana IR, et al. 2021. SARS-CoV-2 Reinfection among Healthcare Workers in Mexico: Case Report and Literature Review. Medicina (Kaunas) 57(5):442 pmid:34063699
- 84. Vora T, Vora P, Vora F, Sharma K, Desai HD. 2021. Symptomatic reinfection with COVID-19: A first from Western India. J Family Med Prim Care 10(3):1496–1498. pmid:34041201
- 85. Sánchez Mollá M, de Gregorio Bernardo C, Ibarra Rizo M, Soriano A. 2021. [Reinfection by SARS-CoV-2 in a socio-sanitary residence. Description of the outbreak]. Aten Primaria 53(8):102100. pmid:34033997
- 86. Fageeh H, Alshehri A, Fageeh H, Bizzoca ME, Lo Muzio L, Quadri MFA. 2021. Re-infection of SARS-CoV-2: A case in a young dental healthcare worker. J Infect Public Health 14(6):685–688. pmid:33971576
- 87. Novazzi F, Baj A, Genoni A, Spezia PG, Colombo A, Cassani G, et al. 2021. SARS-CoV-2 B.1.1.7 reinfection after previous COVID-19 in two immunocompetent Italian patients. J Med Virol 93(9):5648–5649. pmid:33969504
- 88. Letizia AG, Smith DR, Ge Y, Ramos I, Sealfon RSG, Goforth C, et al. 2021. Viable virus shedding during SARS-CoV-2 reinfection. Lancet Respir Med 9(7):e56–e57 pmid:33964243
- 89. Staub T, Arendt V, Lasso de la Vega EC, Braquet P, Michaux C, Kohnen M, et al. 2021. Case series of four re-infections with a SARS-CoV-2 B.1.351 variant, Luxembourg, February 2021. Euro Surveill 26(18):2100423.
- 90. Brehm TT, Pfefferle S, von Possel R, Kobbe R, Nörz D, Schmiedel S, et al. 2021. SARS-CoV-2 Reinfection in a Healthcare Worker Despite the Presence of Detectable Neutralizing Antibodies. Viruses 13(4):661. pmid:33921216
- 91. Konstantinou F, Skrapari I, Bareta E, Bakogiannis N, Papadopoulou AM, Bakoyiannis C. 2021. A Case of SARS-CoV-2 Clinical Relapse after 4 Negative RT-PCR Tests in Greece: Recurrence or Reinfection? Clin Med Insights Case Rep 14:11795476211009813. pmid:33911911
- 92. Shoar S, Khavandi S, Tabibzadeh E, Khavandi S, Naderan M, Shoar N. 2021. Recurrent coronavirus diseases 19 (COVID-19): A different presentation from the first episode. Clin Case Rep 9(4):2149–2152. pmid:33821190
- 93. Rani PR, Imran M, Lakshmi JV, Jolly B, Jain A, Surekha A, et al. 2021. Symptomatic reinfection of SARS-CoV-2 with spike protein variant N440K associated with immune escape. J Med Virol 93(7):4163–4165. pmid:33818797
- 94. Váncsa S, Dembrovszky F, Farkas N, Szakó L, Teutsch B, Bunduc S, et al. 2021. Repeated SARS-CoV-2 Positivity: Analysis of 123 Cases. Viruses 13(3):512 pmid:33808867
- 95. Das P, Satter SM, Ross AG, Abdullah Z, Nazneen A, Sultana R, et al. 2021. A Case Series Describing the Recurrence of COVID-19 in Patients Who Recovered from Initial Illness in Bangladesh. Trop Med Infect Dis 6(2):41. pmid:33807247
- 96. Fintelman-Rodrigues N, da Silva APD, Dos Santos MC, Saraiva FB, Ferreira MA, Gesto J, et al. 2021. Genetic Evidence and Host Immune Response in Persons Reinfected with SARS-CoV-2, Brazil. Emerg Infect Dis 27(5):1446–1453. pmid:33797393
- 97. Teka IA, BenHasan MH, Alkershini AA, Alatresh OK, Abulifa TA, Lembagga HA, et al. 2021. Reinfection with SARS-CoV-2: A case report from Libya. Travel Med Infect Dis 41:102040 pmid:33775916
- 98. Roy S. 2021. COVID-19 Reinfection in the Face of a Detectable Antibody Titer. Cureus 13(3):e14033. pmid:33767941
- 99. Fernandes AC, Figueiredo R. 2021. SARS-CoV-2 reinfection: a case report from Portugal. Rev Soc Bras Med Trop 54:e0002–2021. pmid:33759910
- 100. Ul-Haq Z, Khan A, Fazid S, Noor F, Yousafzai YM, Sherin A. 2020. First documented reinfection of SARS-COV-2 in second wave from Pakistan. J Ayub Med Coll Abbottabad 32(Suppl 1)(4):S704–S705. pmid:33754536
- 101. Krishna VN, Ahmad M, Overton ET, Jain G. 2021. Recurrent COVID-19 in Hemodialysis: A Case Report of 2 Possible Reinfections. Kidney Med 3(3):447–450. pmid:33748738
- 102. Leung S, Hossain N. 2021. Recurrence and Recovery of COVID-19 in an Older Adult Patient with Multiple Comorbidities: A Case Report. Gerontology 67(4):445–448. pmid:33744883
- 103. Salehi-Vaziri M, Jalali T, Farahmand B, Fotouhi F, Banifazl M, Pouriayevali MH, et al. 2021. Clinical characteristics of SARS-CoV-2 by re-infection vs. reactivation: a case series from Iran. Eur J Clin Microbiol Infect Dis 40(8):1713–1719. pmid:33738620
- 104. Romera I, Núñez K, Calizaya M, Baeza I, Molina R, Morillas J. 2021. SARS-CoV-2 reinfection. Med Intensiva (Engl Ed) 45(6):375–376.
- 105. Yadav SP, Wadhwa T, Thakkar D, Kapoor R, Rastogi N, Sarma S. 2021. COVID-19 reinfection in two children with cancer. Pediatr Hematol Oncol 38(4):403–405. pmid:33625290
- 106. Cavanaugh AM, Thoroughman D, Miranda H, Spicer K. 2021. Suspected Recurrent SARS-CoV-2 Infections Among Residents of a Skilled Nursing Facility During a Second COVID-19 Outbreak—Kentucky, July-November 2020. MMWR Morb Mortal Wkly Rep 70(8):273–277. pmid:33630817
- 107. Vetter P, Cordey S, Schibler M, Vieux L, Despres L, Laubscher F, et al. 2021. Clinical, virologic and immunologic features of a mild case of SARS-CoV-2 reinfection. Clin Microbiol Infect 27(5):791.e1–4. pmid:33618012
- 108. Lee JT, Hesse EM, Paulin HN, Datta D, Katz LS, Talwar A, et al. 2021. Clinical and Laboratory Findings in Patients with Potential SARS-CoV-2 Reinfection, May-July 2020. Clin Infect Dis ciab148. pmid:33598716
- 109. Kulkarni O, Narreddy S, Zaveri L, Kalal IG, Tallapaka KB, Sowpati DT. 2021. Evidence of SARS-CoV-2 reinfection without mutations in Spike protein. Clin Infect Dis ciab136. pmid:34492695
- 110. Adrielle Dos Santos L, Filho PGG, Silva AMF, Santos JVG, Santos DS, Aquino MM, et al. 2021. Recurrent COVID-19 including evidence of reinfection and enhanced severity in thirty Brazilian healthcare workers. J Infect 82(3):399–406. pmid:33589297
- 111. Inada M, Ishikane M, Terada M, Matsunaga A, Maeda K, Tsuchiya K, et al. 2021. Asymptomatic COVID-19 re-infection in a Japanese male by elevated half-maximal inhibitory concentration (IC50) of neutralizing antibodies. J Infect Chemother 27(7):1063–1067. pmid:33962861
- 112. Fonseca V, de Jesus R, Adelino T, Reis AB, de Souza BB, Ribeiro AA, et al. 2021. Genomic evidence of SARS-CoV-2 reinfection case with the emerging B.1.2 variant in Brazil. J Infect 83(2):237–279. pmid:34029627
- 113. Zhou X, Zhou YN, Ali A, Liang C, Ye Z, Chen X, et al. 2021. Case Report: A Re-Positive Case of SARS-CoV-2 Associated With Glaucoma. Front Immunol 12:70129 pmid:34394095
- 114. Massachi J, Donohue KC, Kelly JD. 2021. Severe Acute Respiratory Syndrome Coronavirus 2 Reinfection Cases Corroborated by Sequencing. Am J Trop Med Hyg tpmd210365. pmid:34370705
- 115. Massanella M, Martin-Urda A, Mateu L, Marín T, Aldas I, Riveira-Muñoz E, et al. 2021. Critical Presentation of a Severe Acute Respiratory Syndrome Coronavirus 2 Reinfection: A Case Report. Open Forum Infect Dis 8(7):ofab329 pmid:34337095
- 116. Alshukairi AN, El-Kafrawy SA, Dada A, Yasir M, Yamani AH, Saeedi MF, et al. 2021. Re-infection with a different SARS-CoV-2 clade and prolonged viral shedding in a hematopoietic stem cell transplantation patient. Int J Infect Dis 110:267–271. pmid:34289407
- 117. Bader N, Khattab M, Farah F. 2021. Severe reinfection with severe acute respiratory syndrome coronavirus 2 in a nursing home resident: a case report. J Med Case Rep 15(1):392. pmid:34284812
- 118. Awada H, Nassereldine H, Hajj Ali A. 2021. Severe acute respiratory syndrome coronavirus 2 reinfection in a coronavirus disease 2019 recovered young adult: a case report. J Med Case Rep 15(1):382 pmid:34271967
- 119. Zanferrari C, Fanucchi S, Sollazzo MT, Ranieri M, Volterra D, Valvassori L. 2021. Focal Cerebral Arteriopathy in a Young Adult Following SARS-CoV2 Reinfection. J Stroke Cerebrovasc Dis 30(9):105944. pmid:34271279
- 120. Zhang N, Chen X, Jia W, Jin T, Xiao S, Chen W, et al. 2021. Evidence for lack of transmission by close contact and surface touch in a restaurant outbreak of COVID-19. J Infect 83(2):207–216. pmid:34062182
- 121. Naveca FG, Nascimento VA, Nascimento F, Ogrzewalska M, Pauvolid-Corrêa A, Araujo MF, et al. 2021. A case series of SARS-CoV-2 reinfections caused by the variant of concern Gamma in Brazil. medRxiv 2021.11.29.21266109
- 122. Hasanzadeh S, Shariatmaghani SS, Vakilian A, Javan A, Rahmani M, Ganjloo S, et al. 2021. Case series: Reinfection of recovered SARS CoV-2 patients for the third time. Clin Case Rep 9(10):e04936 pmid:34691457
- 123. Pulliam JRC, van Schalkwyk C, Govender N, von Gottberg A, Cohen C, Groome MJ, et al. 2021. Increased risk of SARS-CoV-2 reinfection associated with emergence of the Omicron variant in South Africa. medRxiv 2021.11.11.21266068
- 124. Vitale J, Mumoli N, Clerici P, De Paschale M, Evangelista I, Cei M, et al. 2021. Assessment of SARS-CoV-2 Reinfection 1 Year After Primary Infection in a Population in Lombardy, Italy. JAMA Intern Med e212959
- 125. Babiker A, Marvil CE, Waggoner JJ, Collins MH, Piantadosi A. 2020. The importance and challenges of identifying SARS-CoV-2 reinfections. J Clin Microbiol 59(4):e02769–20.
- 126. Boyton RJ, Altmann DM. 2021. Risk of SARS-CoV-2 reinfection after natural infection. Lancet 397(10280):1161–1163. pmid:33743219
- 127. Hansen CH, Michlmayr D, Gubbels SM, Molbak K, Ethelberg S. 2021. Assessment of protection against reinfection with SARS-CoV-2 among 4 million PCR-tested individuals in Denmark in 2020: a population-level observational study. Lancet 397(10280):1204–1212. pmid:33743221
- 128. Gousseff M, Penot P, Gallay L, Batisse D, Benech N, Bouiller K, et al. 2020. Clinical recurrences of COVID-19 symptoms after recovery: Viral relapse, reinfection or inflammatory rebound? J Infect 81(5):816–846. pmid:32619697
- 129. Lawandi A, Warner S, Sun J, Demirkale CY, Danner RL, Klompas M, et al. 2021. Suspected SARS-CoV-2 Reinfections: Incidence, Predictors, and Healthcare Use among Patients at 238 U.S. Healthcare Facilities, June 1, 2020- February 28, 2021. Clin Infect Dis ciab671
- 130. Iwasaki A. 2020. What reinfections mean for COVID-19. Lancet Infect Dis 2(20):19–20. pmid:33058796
- 131. Leidi A, Koegler F, Dumont R, Dubos R, Zaballa ME, Piumatti G, et al. 2021. Risk of reinfection after seroconversion to SARS-CoV-2: A population-based propensity-score matched cohort study. Clin Infect Dis ciab495
- 132. Hall VJ, Foulkes S, Charlett A, Atti A, Monk EJM, Simmons R, et al. 2021. SARS-CoV-2 infection rates of antibody-positive compared with antibody-negative health-care workers in England: a large, multicentre, prospective cohort study (SIREN). Lancet 397(10283):1459–1469. pmid:33844963
- 133. Abu-Raddad LJ, Chemaitelly H, Malek JA, Ahmed AA, Mohamoud YA, Younuskunju S, et al. 2020. Assessment of the risk of SARS-CoV-2 reinfection in an intense re-exposure setting. Clin Infect Dis ciaa1846
- 134. Ghorbani SS, Taherpour N, Bayat S, Ghajari H, Mohseni P, Hashemi Nazari SS. 2021. Epidemiologic characteristics of cases with re-infection, recurrence and hospital readmission due to COVID-19: a systematic review and meta-analysis. J Med Virol
- 135. Santiago-Espinosa O, Prieto-Torres ME, Cabrera-Gaytán DA. 2021. Laboratory-confirmed SARS-CoV-2 reinfection in the population treated at social security. Respir Med Case Rep 34:101493. pmid:34395189
- 136. Peghin M, Bouza E, Fabris M, De Martino M, Palese A, Bontempo G, et al. 2021. Low risk of reinfections and relation with serological response after recovery from the first wave of COVID-19. Eur J Clin Microbiol Infect Dis 1–8. pmid:34378086
- 137. Wilkins JT, Hirschhorn LR, Gray EL, Wallia A, Carnethon M, Zembower TR, et al. 2021. Serologic Status and SARS CoV-2 Infection over 6-Months of Follow-Up in Healthcare Workers in Chicago: A Cohort Study. Infect Control Hosp Epidemiol 1–29. pmid:34369331
- 138. Ali AM, Ali KM, Fatah MH, Tawfeeq HM, Rostam HM. 2021. SARS-CoV-2 reinfection in patients negative for immunoglobulin G following recovery from COVID-19. New Microbes New Infect 43:100926. pmid:34367645
- 139. Ringlander J, Olausson J, Nyström K, Härnqvist T, Jakobsson HE, Lindh M. Recurrent and persistent infection with SARS-CoV-2—epidemiological data and case reports from Western Sweden, 2020. Infect Dis (Lond). 1–8
- 140. Dobaño C, Ramírez-Morros A, Alonso S, Vidal-Alaball J, Ruiz-Olalla G, Vidal M, et al. 2021. Persistence and baseline determinants of seropositivity and reinfection rates in health care workers up to 12.5 months after COVID-19. BMC Med 19(1):155. pmid:34183003
- 141. Sánchez-Montalvá A, Fernández-Naval C, Antón A, Durà X, Vimes A, Silgado A, et al. 2021. Risk of SARS-CoV-2 Infection in Previously Infected and Non-Infected Cohorts of Health Workers at High Risk of Exposure. J Clin Med 10(9):1968. pmid:34064314
- 142. Lutrick K, Ellingson KD, Baccam Z, Rivers P, Beitel S, Parker J, et al. 2021. COVID-19 Infection, Reinfection, and Vaccine Effectiveness in a Prospective Cohort of Arizona Frontline/Essential Workers: The AZ HEROES Research Protocol. JMIR Res Protoc pmid:34057904
- 143. Crellen T, Pi L, Davis EL, Pollington TM, Lucas TCD, Ayabina D, et al. 2021. Dynamics of SARS-CoV-2 with waning immunity in the UK population. Philos Trans R Soc Lond B Biol Sci 376(1829):20200274 pmid:34053264
- 144. Breathnach AS, Riley PA, Cotter MP, Houston AC, Habibi MS, Planche TD. 2021. Prior COVID-19 significantly reduces the risk of subsequent infection, but reinfections are seen after eight months. J Infect 82(4):e11–e12. pmid:33450303
- 145. O Murchu E, Byrne P, Carty PG, De Gascun C, Keogan M, O’Neill M, et al. 2021. Quantifying the risk of SARS-CoV-2 reinfection over time. Rev Med Virol e2260 pmid:34043841
- 146. Iruretagoyena M, Vial MR, Spencer-Sandino M, Gaete P, Peters A, Delgado I, et al. 2021. Longitudinal assessment of SARS-CoV-2 IgG seroconversionamong front-line healthcare workers during the first wave of the Covid-19 pandemic at a tertiary-care hospital in Chile. BMC Infect Dis 21(1):478 pmid:34039287
- 147. Turner JS, Kim W, Kalaidina E, Goss CW, Rauseo AM, Schmitz AJ, et al. 2021. SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans. Nature 595(7867):421–425. pmid:34030176
- 148. Qureshi AI, Baskett WI, Huang W, Lobanova I, Naqvi SH, Shyu CR. 2021. Re-infection with SARS-CoV-2 in Patients Undergoing Serial Laboratory Testing. Clin Infect Dis ciab345
- 149. Zare F, Teimouri M, Khosravi A, Rohani-Rasaf M, Chaman R, Hosseinzadeh A, et al. 2021. COVID-19 re-infection in Shahroud, Iran: a follow-up study. Epidemiol Infect 149:e159. pmid:33866988
- 150. Fabiánová K, Kyncl J, Vlcková I, Jirincová H, Koštálová J, Liptáková M, et al. 2021. COVID-19 reinfections. Epidemiol Mikrobiol Imunol 70(1):62–67. pmid:33853339
- 151. Davido B, De Truchis P, Lawrence C, Annane D, Domart-Rancon M, Gault E, et al. 2021. SARS-CoV-2 reinfections among hospital staff in the greater Paris area. J Travel Med 28(4):taab058. pmid:33834251
- 152. Brouqui P, Colson P, Melenotte C, Houhamdi L, Bedotto M, Devaux C, et al. 2021. COVID-19 re-infection. Eur J Clin Invest 51(5):e13537 pmid:33675046
- 153. Dimeglio C, Herin F, Miedougé M, Martin-Blondel G, Soulat JM, Izopet J. 2021. Protection of healthcare workers against SARS-CoV-2 reinfection. Clin Infect Dis ciab069. pmid:33503228
- 154. Breathnach AS, Duncan CJA, Bouzidi KE, Hanrath AT, Payne BAI, Randell PA, et al. 2021. Prior COVID-19 protects against reinfection, even in the absence of detectable antibodies. J Infect 83(2):237–279. pmid:34052242
- 155. Rennert L, McMahan C. 2021. Risk of SARS-CoV-2 reinfection in a university student population. Clin Infect Dis ciab454
- 156. Abu-Raddad LJ, Chemaitelly H, Coyle P, Malek JA, Ahmed AA, Mohamoud YA, et al. 2021. SARS-CoV-2 antibody-positivity protects against reinfection for at least seven months with 95% efficacy. EClinicalMedicine 35:100861 pmid:33937733
- 157. Hanrath AT, Payne BAI, Duncan CJA. 2021. Prior SARS-CoV-2 infection is associated with protection against symptomatic reinfection. J Infect 82(4):e29–e30. pmid:33373652
- 158. Lumley SF, O’Donnell D, Stoesser NE, Matthews PC, Howarth A, Hatch SB, et al. 2021. Antibody Status and Incidence of SARS-CoV-2 Infection in Health Care Workers. N Engl J Med 384(6):533–540. pmid:33369366
- 159. Hamed E, Sedeeq S, Alnuaimi AS, Syed M, ElHamid MA, Alemrayat B, et al. 2021. Rates of recurrent positive SARS-CoV-2 swab results among patients attending primary care in Qatar. J Infect 82(4):84–123. pmid:33144191
- 160. Addetia A, Crawford KHD, Dingens A, Zhu H, Roychoudhury P, Huang ML, et al. 2020. Neutralizing Antibodies Correlate with Protection from SARS-CoV-2 in Humans during a Fishery Vessel Outbreak with a High Attack Rate. J Clin Microbiol 58(11):e02107–20. pmid:32826322
- 161. Mack CD, Tai C, Sikka R, Grad YH, Maragakis LL, Grubaugh ND, et al. 2021. SARS-CoV-2 Reinfection: A Case Series from a 12-Month Longitudinal Occupational Cohort. Clin Infect Dis ciab738
- 162. Abu-Raddad LJ, Chemaitelly H, Bertollini R; 2021. National Study Group for COVID-19 Epidemiology. Severity of SARS-CoV-2 Reinfections as Compared with Primary Infections. N Engl J Med NEJMc2108120
- 163. Bean DJ, Monroe J, Turcinovic J, Moreau Y, Connor JH, Sagar M. 2021. SARS-CoV-2 reinfection associates with unstable housing and occurs in the presence of antibodies. Clin Infect Dis ciab940.
- 164. Mensah AA, Campbell H, Stowe J, Seghezzo G, Simmons R, Lacy J, et al. 2021. Risk of SARS-CoV-2 reinfections in children: prospective national surveillance, January 2020 to July 2021, England. medRxiv 2021.12.10.21267372
- 165. Levin-Rector A, Firestein L, McGibbon E, Sell J, Lim S, Lee EH, et al. 2021. Reduced Odds of SARS-CoV-2 Reinfection after Vaccination among New York City Adults, June–August 2021. medRxiv 2021.12.09.21267203
- 166. Malhotra S, Mani K, Lodha R, Bakhshi S, Mathur VP, Gupta P, et al. 2022. SARS-CoV-2 Reinfection Rate and Estimated Effectiveness of the Inactivated Whole Virion Vaccine BBV152 Against Reinfection Among Health Care Workers in New Delhi, India. JAMA Netw Open 5(1):e2142210 pmid:34994793
- 167. Mao Y, Wang W, Ma J, Wu S, Sun F. 2021. Reinfection rates among patients previously infected by SARS-CoV-2: systematic review and meta-analysis. Chin Med J (Engl) 135(2):145–152. pmid:34908003
- 168. Salehi-Vaziri M, Pouriayevali MH, Fotouhi F, Jalali T, Banifazl M, Farahmand B, et al. 2021. SARS-CoV-2 re-infection rate in Iranian COVID-19 cases within one-year follow-up. Microb Pathog 161(Pt B):105296 pmid:34801646
- 169. Mensah AA, Lacy J, Stowe J, Seghezzo G, Sachdeva R, Simmons R, et al. 2022. Disease severity during SARS-COV-2 reinfection: a nationwide study. J Infect S0163-4453(22)00010–X pmid:35085659
- 170. McKeigue PM, McAllister DA, Robertson C, Stockton D, Colhoun HM, for the PHS COVID-19 Epidemiology and Research Cell. 2021. Reinfection with SARS-CoV-2: outcome, risk factors and vaccine efficacy in a Scottish cohort. medRxiv 2021.11.23.21266574
- 171. Maier HE, Balmaseda A, Ojeda S, Cerpas C, Sanchez N, Plazaola M, et al. 2021. An immune correlate of SARS-CoV-2 infection and severity of reinfections. medRxiv 2021.11.23.21266767 pmid:34845458
- 172. Goldberg Y, Mandel M, Bar-On YM, Bodenheimer O, Freedman L, Ash N, et al. 2021. Protection and waning of natural and hybrid COVID-19 immunity. medRxiv 2021.12.04.21267114
- 173. Chivese T, Matizanadzo JT, Musa OAH, Hindy G, Furuya-Kanamori L, Islam N, et al. 2021. The prevalence of adaptive immunity to COVID-19 and reinfection after recovery—a comprehensive systematic review and meta-analysis. medRxiv 2021.09.03.21263103
- 174. Shinde V, Bhikha S, Hoosain Z, Archary M, Bhorat Q, Fairlie L, et al. 2021. Efficacy of NVX-CoV2373 Covid-19 Vaccine against the B.1.351 Variant. N Engl J Med 384(20):1899–1909. pmid:33951374
- 175. Tegally H, Wilkinson E, Giovanetti M, Iranzadeh A, Fonseca V, Giandhari J, et al. 2021. Detection of a SARS-CoV-2 variant of concern in South Africa. Nature 592(7854):438–443. pmid:33690265
- 176. Muik A, Lui BG, Wallisch AK, Bacher M, Mühl J, Reinholz J, et al. 2022. Neutralization of SARS-CoV-2 Omicron by BNT162b2 mRNA vaccine-elicited human sera. Science 375(6581):678–680 pmid:35040667
- 177. Dejnirattisai W, Huo J, Zhou D, ZahradnÃk J, Supasa P, Liu C, et al. 2022. SARS-CoV-2 Omicron-B.1.1.529 leads to widespread escape from neutralizing antibody responses. Cell 185(3):467–484.e15 pmid:35081335
- 178. Hui KPY, Ho JCW, Cheung MC, Ng KC, Ching RHH, Lai KL, et al. 2022. SARS-CoV-2 Omicron variant replication in human bronchus and lung ex vivo. Nature. pmid:35104836
- 179. Meng B, Abdullahi A, Ferreira IATM, Goonawardane N, Saito A, Kimura I, et al. 2022. Altered TMPRSS2 usage by SARS-CoV-2 Omicron impacts tropism and fusogenicity. Nature. pmid:35104837
- 180. Altarawneh H, Chemaitelly H, Tang P, Hasan MR, Qassim S, Ayoub HH, et al. 2022. Protection afforded by prior infection against SARS-CoV-2 reinfection with the Omicron variant. medRxiv 2022.01.05.22268782
- 181. Nunes MC, Sibanda S, Baillie VL, Kwatra G, Aguas R, Madhi SA, et al. 2022. SARS-CoV-2 Omicron symptomatic infections in previously infected or vaccinated South African healthcare workers. medRxiv 2022.02.04.22270480 pmid:35335091
- 182. Lyngse FP, Mortensen LH, Denwood MJ, Christiansen LE, Moller CH, Skov RL, et al. 2021. SARS-CoV-2 Omicron VOC Transmission in Danish Households. medRxiv 2021.12.27.21268278
- 183. Lacy J, Mensah A, Simmons R, Andrews M, Siddiqui MR, Bukasa A, et al. 2022. Protective effect of a first SARS-CoV-2 infection from reinfection: a matched retrospective cohort study using PCR testing data in England. medRxiv 2022.01.10.22268896; pmid:35607808
- 184. Rangachev A, Marinov GK, Mladenov M. 2021. The demographic and geographic impact of the COVID pandemic in Bulgaria and Eastern Europe in 2020. medRxiv 2021.04.06.21254958
- 185. Karlinsky A, Kobak D. 2021. Tracking excess mortality across countries during the COVID-19 pandemic with the World Mortality Dataset. Elife 10:e69336 pmid:34190045
- 186. Shu Y, McCauley J. 2017. GISAID: Global initiative on sharing all influenza data—from vision to reality. Euro Surveill 22(13):30494 pmid:28382917
- 187. Kraemer MUG, Hill V, Ruis C, Dellicour S, Bajaj S, McCrone JT, et al. 2021. Spatiotemporal invasion dynamics of SARS-CoV-2 lineage B.1.1.7 emergence. 2021. Science 373(6557):889–895 pmid:34301854
- 188. Davies NG, Abbott S, Barnard RC, Jarvis CI, Kucharski AJ, Munday JD, et al. 2021. Estimated transmissibility and impact of SARS-CoV-2 lineage B.1.1.7 in England. Science 372(6538):eabg3055 pmid:33658326
- 189. Mlcochova P, Kemp SA, Dhar MS, Papa G, Meng B, Ferreira IATM, et al. 2021. SARS-CoV-2 B.1.617.2 Delta variant replication and immune evasion. Nature 599(7883):114–119. pmid:34488225
- 190. Hightower AW, Orenstein WA, Martin SM. 1988. Recommendations for the use of Taylor series confidence intervals for estimates of vaccine efficacy. Bull World Health Organ 66(1):99–105. pmid:3260147
- 191. Cohn BA, Cirillo PM, Murphy CC, Krigbaum NY, Wallace AW. 2022. SARS-CoV-2 vaccine protection and deaths among US veterans during 2021. Science 375(6578):331–336. pmid:34735261
- 192. Bar-On YM, Goldberg Y, Mandel M, Bodenheimer O, Freedman L, Alroy-Preis S, et al. 2021. Protection against Covid-19 by BNT162b2 Booster across Age Groups. 2021. N Engl J Med 385(26):2421–2430. pmid:34879188
- 193. Collier DA, Ferreira IATM, Kotagiri P, Datir RP, Lim EY, Touizer E, et al. 2021. Age-related immune response heterogeneity to SARS-CoV-2 vaccine BNT162b2. Nature 596(7872):417–422. pmid:34192737