Introduction

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-COV-2), which was found in China in 2019. The virus spread rapidly, and the World Health Organization declared a pandemic on March 11, 2020. As of April 4. 2022, about 490 million people worldwide have been infected and about six million people have died from COVID-19 [1]. Acute pneumonia is a major symptom of COVID-19, but SARS-COV-2 can affect various organs. SARS-COV-2 infection leads to various diseases such as taste dysfunction, meningitis, myocarditis, and arterial and venous thromboembolism [2–5]. The mechanisms by which COVID-19 leads to thrombosis and thromboembolism have remained unclear. It has been thought that endothelial dysfunction potentially contributes to thrombosis events [6].

Endothelial dysfunction caused by a decrease in nitric oxide (NO) bioavailability through imbalances between pro-inflammation and anti-inflammation and pro-oxidative stress and anti-oxidative stress is the first step of atherosclerosis [7–9]. Atherosclerosis progresses asymptomatically, finally leading to cardiovascular (CV) events [7, 10]. Rapid endothelial dysfunction also may contribute to thrombosis and thromboembolism [11]. Measurement of flow-mediated vasodilation (FMD) in the brachial artery is the most popular noninvasive tool for assessment of endothelial function. It has been shown that every 1% decrease in FMD is associated with a 10% increase in the risk of CV events [12]. On the other hand, nitroglycerine-induced vasodilation (NID) reflects vascular smooth muscle function.

The effectiveness of Covid vaccines have been established by clinical trials and real-world data [13, 14]. BNT162b2 (Comirnaty®; BioNTech and Pfizer) is one of the nucleoside-modified messenger ribonucleic acid (mRNA) vaccines for COVID-19. In Japan, 80% of subjects have received the 2^nd dose vaccine as of Mar. 31. 2022. In America, 66% of subjects have received the 2^nd dose vaccines as of Mar. 31. 2022 [15]. However, the number of new people receiving vaccination seems to have reached a plateau [15]. One reason for the lack of progress in vaccination may lie in concerns about serious adverse effects including CV events. Currently, there are no data on the long-term adverse effects of vaccines since BNT 162b2 vaccination started in December 2020. Therefore, in the present study, we assessed the effects of BNT162b2 vaccines on vascular function using FMD and NID as surrogate markers for CV events.

Methods

Results

Baseline characteristics of the subjects

The baseline characteristics of the 23 subjects are summarized in Table 1. The mean age of the subjects was 36 years. The 23 subjects included 16 men. One subject had hypertension and 2 subjects had dyslipidemia.

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Table 1. Clinical characteristics of subjects.

https://doi.org/10.1371/journal.pone.0302512.t001

Effect of BNT162b2 vaccine on endothelial function

Fig 1A shows changes in FMD before vaccination and during the follow-up periods after vaccination. FMD was significantly smaller at two weeks after the 2^nd dose of vaccination than before vaccination (6.5±2.4% and 8.2±2.6%, p = 0.03), and FMD was significantly larger at six months than at two weeks after the 2^nd dose of vaccination (8.2±3.0% and 6.5±2.4%, p = 0.03). There was no significant difference between FMD before vaccination and FMD at six months after the 2^nd dose of vaccination (8.2±2.6% to 8.2±3.0%, p = 0.96).

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Fig 1.

Dot graphs show effects of the BNT162b2 mRNA Covid-19 vaccine on flow-mediated vasodilation (A) and nitroglycerine-induced vasodilation (B) before vaccination and at two weeks and six months after the 2^nd dose of vaccination.

https://doi.org/10.1371/journal.pone.0302512.g001

Discussion

We demonstrated for the first time that endothelial function was impaired by BNT162b2 mRNA Covid-19 vaccination and returned to the baseline level within six months after vaccination and that BNT162b2 mRNA Covid-19 vaccination did not alter vascular smooth muscle function.

The efficacy of the BNT162b2 mRNA Covid-19 vaccine is well established. A previous study showed that two doses of BNT162b2 vaccine reduced the occurrence of Covid-19 by 95% compared with that in a placebo group [14]. However, various adverse events have been reported to occur within a short period of time after BNT162b2 mRNA Covid-19 vaccination [14]. A few subjects had severe adverse events after receiving the BNT162b2 mRNA Covid-19 vaccine [14]. Mevorach et al. reported that the incidence of myocarditis increased after the 2^nd dose of vaccination in young male subjects [19]. However, the long-term effects of the BNT162b2 mRNA Covid-19 vaccine on organ damage and incidence of CV events are still uncertain. Several studies including our study have shown that endothelial function assessed by FMD is a surrogate marker for organ damage and cardiovascular events [20, 21]. FMD was significantly smaller at two weeks after the 2^nd dose of vaccination than before vaccination. FMD had returned to the baseline level at six months after the 2^nd dose of vaccination. NID before vaccination was similar to that during the follow-up periods after vaccination. These results suggest that the BNT162b2 mRNA Covid-19 vaccine impairs endothelial function but not vascular smooth muscle function early post-vaccination and that the BNT162b2 mRNA Covid-19 vaccine-induced endothelial dysfunction is restored within six months after vaccination.

In the present study, we confirmed that the BNT162b2 mRNA Covid-19 vaccine impaired endothelial function in relatively healthy subjects and that the BNT162b2 mRNA Covid-19 vaccine-induced endothelial dysfunction was restored to the baseline level within six months after the 2^nd dose of vaccination. Although long-term effects of the BNT162b2 mRNA Covid-19 vaccine on CV events may be limited, endothelial dysfunction may be, at least in part, involved in thrombotic events that develop relatively early after Covid-19 vaccination. In addition, we cannot deny the possibility that harmful effects of the BNT162b2 mRNA Covid-19 vaccine on vascular function are stronger in patients with advanced atherosclerosis than in healthy individuals and that Covid-19 vaccination-induced impairment of vascular function is prolonged in those patients. Future studies are needed to confirm the short-term and long-term effects of Covid-19 vaccination on vascular function in individuals with high cardiovascular risk factors and patients with cardiovascular disease.

This study has potential limitations. First, this study was a single-center study with a small sample size and was conducted in only medical staff. In addition, it is clinically important to evaluate the effects of vaccination on vascular function in patients with cardiovascular risk factors including hypertension, dyslipidemia, and diabetes mellitus. Unfortunately, only one subject with dyslipidemia and one subject with dyslipidemia and hypertension were included in the present study. Future studies are needed to confirm the roles of vaccination in vascular function in patients who have cardiovascular risk factors and cardiovascular disease in a large study population. However, we confirmed significant changes in FMD during a six-month follow-up period after vaccination. Second, we did not have information on blood biochemistry at each time point when vascular function was assessed. Measurements of inflammatory markers, antibodies to Covid-19 vaccine and immune markers would enable more specific conclusions concerning the roles of Covid-19 vaccine in vascular function to be drawn. Third, in the present study, we could not use placebo due to ethical issues.

Conclusions

In conclusion, BNT162b2 mRNA Covid-19 vaccine temporally impaired endothelial function and the impaired endothelial function returned to the baseline level within six months after the 2^nd dose of vaccination. Although long-term effects of BNT162b2 mRNA Covid-19 vaccine on CV events may be limited, endothelial dysfunction may be, at least in part, involved in thrombotic events that develop relatively early after Covid-19 vaccination.

Supporting information

Acknowledgments

The authors would like to thank all of the patients who participated in this study. In addition, we thank Megumi Wakisaka, Ki-ichiro Kawano and Satoko Michiyama for their excellent secretarial assistance.