Introduction

Vaccination has long been recognized as a paramount public health intervention, playing a crucial role in preventing and controlling infectious diseases across all age groups—from children to adults [1,2]. Vaccines significantly contribute to population health by reducing the incidence of preventable diseases, lowering morbidity and mortality rates, and fostering overall health status [3]. Interruptions in vaccination programs can lead to the accumulation of susceptible individuals within the general population, thereby heightening the risk of the resurgence of diseases that were previously under control or eliminated [1].

Primary care plays a pivotal role in vaccination services, encompassing the administration of vaccines and the provision of patient counseling regarding the risks and benefits of vaccination for various indications [4]. It is also integral to the delivery of preventive services, and patients with access to primary care are more likely to stay informed about a spectrum of preventive measures [5]. The COVID-19 pandemic disrupted primary care and various preventive services, including vaccinations [6–10]. Disparities in the receipt of preventive health care services have long been noted, with disadvantaged groups often experiencing lower vaccination rates [7,11]. Current evidence indicates that disruptions caused by COVID-19 have further widened these disparities, particularly affecting vulnerable groups [12–15]. Factors such as socioeconomic status, race/ethnicity, place of residence, educational attainment, and insurance status are associated with reduced vaccination rates [2,3].

Numerous studies have investigated changes in vaccination rates during the pandemic, revealing a significant decline of up to 94% compared to pre-pandemic rates [11,14–23]. Although these changes varied over time, the most pronounced decrease occurred in the first month. While some studies have indicated subsequent improvements in vaccination rates, this recovery has been inconsistent. Notably, most research has focused exclusively on pediatric populations in specific regions [16–18,22]. There is limited evidence assessing the effects of the pandemic on vaccination across all age groups in primary care settings. In a nationwide study included commercially insured individuals of all age groups, findings revealed a decrease in vaccination rates across all ages [11].

While most prior research has focused on pediatric immunizations, there is a need to examine vaccination trends across the life course. Adolescents and adults are also recommended to receive routine immunizations, including tetanus, diphtheria, and acellular pertussis (Tdap), human papillomavirus (HPV), meningococcal vaccines, influenza, and pneumococcal vaccines. Missed or delayed administration of these vaccines during the pandemic may increase susceptibility to preventable diseases, including outbreaks in older populations with comorbidities.

While current evidence has shown declines in vaccination rates during the COVID-19 pandemic, most studies focus on pediatric populations or specific regions. Our objective was to assess the impact of the COVID-19 pandemic on non-COVID-19 vaccination services delivered through primary care for various subpopulations, including children, adolescents, and adults.

Methods

Results

Fig 1 shows the number of vaccinated individuals, categorized by age group, across three distinct periods. The number of vaccinated individuals decreased by 9.6% among children-adolescents and 4.2% among adults in Pandemic Year 1. This decline became more pronounced in Pandemic Year 2, with a 19.4% decrease among children-adolescents and a 14.2% decrease among adults compared to the Pre-Pandemic Year.

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Fig 1. Vaccination status of child-adolescent and adult individuals across pre-pandemic and pandemic years.

https://doi.org/10.1371/journal.pone.0325934.g001

Table 1 indicates the distribution of study population characteristics by vaccination status. In the pre-pandemic year, 49.7% of vaccinated child-adolescent individuals were female, 63.0% were white, 67.5% of them resided in urban areas and 52.9% had an SDI < 51. For adults, 56.1% were female, 81.2% were white, 77.8% of them resided in urban areas and 55.2% had an SDI < 51. In Pandemic Y1, 49.6% of vaccinated child-adolescent individuals were female, 61.2% were white, 67.5% of them resided in urban areas and 51.6% had an SDI < 51. For adults, 55.8% were female, 81.2% were white, 79.1% of them resided in urban areas, and 56.2% had an SDI < 51. In Pandemic Y2, 49.6% of vaccinated child-adolescent individuals were female, 58.3% were white, 68.1% of them resided in urban areas, and 50.6% had an SDI < 51. For adults, 55.8% were female, 80.2% were white, 79.4% of them resided in urban areas, and 55.5% had an SDI < 51. Vaccination status comparisons for each variable, within each age group and study period, were statistically significant (p < 0.001).

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Table 1. Distribution of study population characteristics by vaccination status in each study period.

https://doi.org/10.1371/journal.pone.0325934.t001

Compared to that of Pre-Pandemic Year, there was a decline in the total number of vaccine doses administered during the pandemic (S2 Table). Among children and adolescents, the administered vaccine doses decreased by 9.6% in Pandemic Y1 and 14.9% in Pandemic Y2. For adults, a similar trend was observed, with decreases of 4.7% and 15.3%, respectively, during the same period.

Fig 2 compares the differences in vaccination and visit rates for all patients between the two Pandemic Years and the Pre-Pandemic Year. Overall, the monthly visit and vaccination rates declined during the pandemic compared to the those of the Pre-Pandemic Year, with a few exceptions. During Pandemic Y1, both visit and vaccination rates improved only in certain months (visits: June, September and December; vaccinations: August, and September) compared to those the Pre-Pandemic Year. Throughout Pandemic Y2, visits exceeded pre-pandemic levels in just three months (March, June, and December), whereas vaccination rates remained consistently lower, except in June and November. Despite a partial recovery in visit rates during Pandemic Y2, vaccination rates continued to be low. With the exception of August and September in the 1st year and May, June and November in the 2nd year, differences in vaccination rates were worse than visit rates during the remaining months of the pandemic. While the monthly trends in vaccination and visit rates were similar among adults compared to overall sample, except May and July in the 2nd year, the child-adolescent group had different trends in both years (S1 and S2 Figs). In both years, visit rates decreased more than vaccination rates in four months (April, May, October and February in the 1st year and March, May, June and February in the 2nd year).

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Fig 2. Changes in vaccination and visit rates during pandemic years compared with the pre-pandemic period.

https://doi.org/10.1371/journal.pone.0325934.g002

In logistic regression models, as presented in Model 1, females, rural residents, and individuals living in areas with higher (SDI > 50) social risk had the lowest odds of vaccination in all three time periods (p < 0.05 in each period) (Table 2). This pattern persisted even after introducing age adjustment in Model 2, where females, rural residents and individuals living in areas with higher (SDI > 50) social risk maintained the lowest odds of vaccination before and during the pandemic (p < 0.05). As the pandemic continued, individuals living in rural areas had lower odds of being vaccinated in both models, whereas the odds remained similar within groups with higher social risk.

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Table 2. Logistic regression models estimating the odds ratio for vaccination in each period.

https://doi.org/10.1371/journal.pone.0325934.t002

Discussion

Receipt of non-COVID-19 vaccines through primary care declined significantly during the pandemic. These declines were consistent across age groups—children, adolescents, and adults—and persisted over time. This pattern aligns with prior studies showing substantial disruptions in routine immunizations during the early stages of the COVID-19 pandemic, as in-person care was postponed or avoided [6–9]. Although some recoveries were noted, it was inconsistent, with disparities persisting among vulnerable groups. Some studies showed that childhood vaccination rates remained below pre-pandemic levels into 2021, particularly among lower-income and racially or ethnically minoritized populations [27–30]. Our study contributes to this literature by focusing specifically on primary care settings and by examining vaccination trends across rural and socioeconomically disadvantaged populations, highlighting the potential for lasting declines in vaccine uptake in these communities.

Primary care visits also declined during the pandemic, across all age groups, with a partial recovery in Pandemic Year 2. A study examining COVID-19 vaccinations from the same database for 2021 also showed a decline in patient visits, which reduced the opportunity for vaccination [30]. In a nationwide study similar to ours, visit rates improved faster than vaccination rates across all age groups [11]. Although reduced in-person care and the rise of telehealth may have contributed to missed vaccinations [31], our results suggest that reduced access alone does not fully explain the sustained drop in vaccination rates.

A notable exception to the overall trend was a sharp spike in vaccinations observed in August 2020, likely reflecting a seasonal surge in back-to-school immunizations. Many schools and local authorities continued to enforce vaccine requirements despite the pandemic, prompting families to seek care during this period. Eased restrictions in some areas may have also contributed to a temporary increase in in-person visits. However, this rebound was short-lived and did not lead to sustained recovery, especially among adults and patients in rural or socioeconomically deprived areas.

Our analysis of patient characteristics highlighted trends consistent with earlier literature: rural residents, and those living in areas of high social deprivation were less likely to receive vaccines across all time periods [7,9]. Rural residents, however, appear particularly at risk for low vaccination rates after the onset of the pandemic. We found that individuals living in rural areas had even lower odds of vaccine receipt in Pandemic Year 2 compared with Pandemic Year 1. These findings underscore the need for targeted outreach and support for rural populations, where structural barriers and limited access to care may compound pandemic-related disruptions.

While these trends suggest meaningful gaps in vaccine delivery, changes in the composition of patients visiting primary care may also help explain the observed trends. For instance, individuals who sought care during the pandemic may differ in age, health status, or vaccine eligibility from those who delayed care [32,33]. Shifts in visit type—from preventive to acute—could also reduce opportunities for vaccination. However, the persistence of declines across subgroups and time periods supports the interpretation that structural disruptions in care delivery were a key driver.

Our findings have several implications for clinical practice and public health. Catch-up vaccination efforts are urgently needed, particularly in rural and socioeconomically disadvantaged communities. Strategies could include mobile clinics, school-based drives, and reminder systems. At the policy level, stronger support is needed to help primary care practices sustain essential preventive services during public health crises. Enhancing standardized reporting tools, reminders, and patient outreach systems could help clinicians more effectively identify and reach under-vaccinated individuals. These efforts are critical to ensuring continuity of care and preventing widening immunization gaps during future disruptions.

Our study contributes to a growing body of literature on the impact of the COVID-19 pandemic on overall vaccination rates. Similar to other studies, our results suggest consistent declines of vaccinations across all age groups. Particular strengths of our study are the use of a national sample of registry data (claims and electronic health records) from primary care settings, a full two years’ follow-up data to onset of the pandemic, and detailed patient characteristics to identify vulnerable subgroups with a modest proportion of rural individuals each year (20–35%).

A number of study limitations should be noted. First, primary care participation in the PRIME registry is voluntary and not necessarily representative of all primary care practices across the country. Second, PRIME data capture the encounters for participating practices, rather than a consistent set of patients over time. Thus, our study data contain repeated cross-sectional information rather than a longitudinal cohort of the same individuals over time and an individual might be unique within each time period. Finally, it is important to note that PRIME data only capture care provided by primary care practices, we cannot rule out the possibility that individuals may have shifted their site of care for receipt of vaccinations in response to the pandemic.

Conclusions

Our study provides further evidence that the COVID-19 pandemic was associated with declines in vaccination rates. It is noteworthy that despite the improvement in visits, the decline in vaccination rates persisted into the second year of the pandemic. These declines will increase risk of outbreaks of vaccine-preventable diseases, resurgence of diseases that were previously under control or eliminated, and additional health disparities for immunocompromised individuals. We also find evidence that individuals in rural areas may be particularly at risk for declining vaccination rates, highlighting an important target population for new programs and interventions.

Supporting information