A team of scientists from Spain has recently evaluated the immune responses induced by mRNA-based Pfizer/BioNTech coronavirus disease 2019 (COVID-19) vaccine in healthcare workers with or without a history of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.
The study findings reveal that immune memory developed in response to previous SARS-CoV-2 infection can persist for a long time and that only a single vaccine dose is sufficient to induce robust antibody response among previously infected individuals.
A preprint version of the study is available on the medRxiv* server, while the article undergoes peer review.
Vaccines developed against COVID-19 have provided immense public health benefits by shielding the global population from deadly SARS-CoV-2. According to the World Health Organization (WHO) report, more than 1.5 billion vaccine doses have already been administered globally. By analyzing potential risk factors, most countries have prioritized vaccine distribution to the most susceptible subgroups of the population. However, given the shortage in vaccine supply, a more accurate vaccine prioritization is urgently required to achieve the highest healthcare benefits.
In the current study, the scientists have evaluated vaccine-induced immune responses in healthcare workers with or without prior SARS-CoV-2 exposure.
According to available literature, anti-SARS-CoV-2 immunity developed in response to natural infection persists for up to 10 months. Moreover, a low rate of reinfection and disease recurrence has been observed among COVID-19 recovered individuals. Given these findings, the scientists have hypothesized that individuals with previous SARS-CoV-2 infection may not require immediate vaccination for protection, or alternatively, a single vaccine dose may be sufficient for them to provide protection.
A total of 63 healthcare workers participated in the study. Among them, 33 were previously infected with SARS-CoV-2, and 30 were without prior infection. Among previously infected participants, 22 were mildly symptomatic, 6 had pneumonia, and 5 were asymptomatic.
All study participants received 2 doses of the mRNA-based COVID-19 vaccine developed by Pfizer/BioNTech. Previously infected participants received the 1st vaccine dose about 10 months after COVID-19 diagnosis.
The blood samples collected from participants were analyzed for IgG-specific anti-spike receptor-binding domain (RBD) antibodies. Overall, the antibody levels were measured at 7 time points: at baseline before vaccination; at 7, 14, and 21 days after the 1st dose; and at 7, 14, and 21 days after the 2nd dose.
To determine the durability of antibody response, a separate set of measurements was done 8 – 10 weeks after the 2nd vaccine dose.
At baseline, 29 out of 33 healthcare workers with previous infection showed detectable anti-SARS-CoV-2 antibody levels. Only 4 participants were seronegative. Interestingly, both seropositive and seronegative participants exhibited a 126-fold increase in antibody levels 7 days after receiving the 1st vaccine dose. However, only a slight increase in antibody levels was observed in these participants at day 14 post-vaccination, followed by no increase at day 21 post-vaccination.
In contrast, participants without prior SARS-CoV-2 infection showed a seronegative status at baseline. Only 5 of them showed detectable antibody levels after 7 days of vaccination. However, at day 14, all participants showed detectable antibody levels, which continued to increase and reached a 1.6-fold higher levels at day 21 post-vaccination.
Regarding 2nd vaccine dose, no significant change in antibody levels was observed at any time points in participants with prior SARS-CoV-2 infection. In contrast, a 16-fold increase in antibody level was observed in participants without prior infection at day 7 post-vaccination, which remained stable up to day 14. However, at day 21, the participants exhibited reduced antibody levels.
At all experimental time points, previously infected participants exhibited significantly higher antibody levels than those without prior infection. Furthermore, four previously infected participants who did not receive the 2nd vaccine dose showed comparable antibody levels to those who completed the 2-dose vaccination regimen.
Regarding long-lasting immunity, a considerable reduction in antibody level was observed in all participants 2 months after the 2nd vaccine dose. The reduction was more prominent in participants without prior infection.
Regarding vaccine-related adversities, previously infected participants showed more side effects after the 1st vaccine dose compared to those without prior infection. However, no such difference was observed between the two study groups after the 2nd vaccine dose. In general, the vaccine did not cause any serious adversities among study participants.
The study findings reveal that even after 10 months of recovery, individuals with prior SARS-CoV-2 exposure are capable of inducing strong secondary immunity in response to a single vaccine dose. Based on the study findings, the scientists suggest that vaccination of COVID-19 recovered individuals can be postponed to prioritize high-risk populations for vaccination.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.