ABSTRACT
Aims: Healthcare workers are at increased risk of SARS-CoV-2 infection and were among the first to be vaccinated against the virus. We aimed to estimate the level and duration of protection the vaccines provide against infection by monitoring the humoral immune response mounted after each vaccination. Method(s): 177 and 102 respiratory health professionals were recruited before receiving initial Pfizer-Biontech and booster vaccines, respectively. Serum levels of RBD-specific IgG antibodies were measured at various time points;the unit of measurement was signal/cut-off (S/CO). Result(s): In previously uninfected participants, IgG production was slow to start in response to the first vaccination and only reached the positive range shortly before the second vaccination on day 21. Following the first vaccination, IgG production peaked on day 28, whereas following the booster vaccination IgG levels peaked more rapidly but at a significantly lower level (43.7 vs. 22.0 S/CO, p<0.0001). Stratification by sex and mean age showed no difference in maximum IgG levels. In most participants, IgG levels declined rapidly after both the initial and booster vaccination, but 4 months after vaccination, the booster vaccine provided a significantly higher proportion of circulating IgG compared to the maximum level (30.6% vs. 21.9%). The number of COVID-positive cases 4 months after vaccination was higher for the booster vaccine. Conclusion(s): Based on IgG titers, the Pfizer-Biontech booster vaccine appears to provide a longer-lasting humoral immune response compared to the first vaccination, but this may still confer less protection against new virus variants.
ABSTRACT
Background: SARS-CoV-2 vaccines are expected to induce both cellular and humoral immune responses, however, the dynamics and correlation between the two types of immunity are not precisely understood. Aim(s): Assessing IgG levels and T-cell response induced by SARS-CoV-2 vaccines and investigating the correlation between cellular and humoral immune responses. Method(s): Blood samples were taken from 166 respiratory healthcare professionals at four time-points: first before administering the booster vaccine, then on day 28, 56 and 120 post-vaccination. For the assessment of humoral immune response anti-Spike protein IgG ELISA was used, while T-cell response was tested by interferon-gammarelease-assay. Result(s): Out of 166 patients, 120 individuals presented positive result for interferon-gamma, while 100 had positive results for IgG. The positivity rate of cellular immune response was found to be significantly higher than humoral between the second and third doses of anti-COVID vaccines (P<0,05). Participants, who have had SARS-CoV-2 infection before the first two shots, the immune response was detectable at a statistically higher rates than in the COVID naive group. The third dose triggered different dynamics regarding the IgG titers and T-cell response. Four months after the administration of the booster shot both humoral and cellular immune response were detectable simultaneously. Conclusion(s): After the first two doses, the cellular immune response was found to last longer than humoral, especially in previously infected individuals. Measuring the T-cell responses to SARS-CoV-2 vaccines may complement the antibody tests currently used in clinical practice.