Assessment of antibody titer and side effects after fourth doses of COVID-19 mRNA vaccination in 38 healthy volunteers

ObjectivesFourth dose of SARS-CoV-2 vaccination was started from the end of May, 2022 in Japan. However, data on the precise analysis of the side effects after fourth vaccination, remain scarce. Here, we examined the side effects and the levels of SARS-CoV-2 antibody titers in healthy volunteers who underwent BNT162b2 vaccination for the fourth time.MethodsThirty-eight volunteers were assessed for the side effects of the vaccination for the fourth dose, and samples were used for the measurement of SARS-CoV-2 IgG and IgM antibody with chemiluminescent assays.ResultsWe found that the level of IgG at day 504 (average, 117.9 AU/mL [SD 76.9]), was significantly higher than at day 264 (average, 17.3 AU/mL [SD 13.1]), which are 8 months after the third and second vaccination, respectively. The level of IgG was potently increased after fourth vaccination (average, 711.8 AU/mL [SD 361.9]), whereas IgM remained baseline level. Commonly reported side effects in the participants after the fourth dose were similar to those until third dose, such as sore arm/pain (81.0 %), generalized weakness/fatigue (57.1 %) and fever (54.8 %). The number of side effects were significantly decreased with age, and participant with sore arm/pain had higher IgG titer (p=0.0007), whereas participant with lymphadenopathy had lower IgG (p=0.0371).ConclusionsThe level of IgG was significantly higher in 8 months after the third, compared to the second, vaccination, and it was potently increased after fourth vaccination. The number of side effects were inversely correlated with age. Sore arm/pain and lymphadenopathy may affect IgG titer.