Measurement of multiple SARS-CoV-2 antibody titer after vaccination represents individual vaccine response and contributes to individually appropriate vaccination schedules

Ota, K.; Yanagihara, K.; Murakami, S.; Mukae, H.; Kohno, S.

mRNA vaccine (BNT162b2) induces antibodies against Spike protein produced by host cell. However, multiple antibody responses before and after vaccination have not been clarified. To clarify multiple antibody responses after mRNA vaccination in a variation of individuals including prior infection of COVID-19. This is a prospective, observational study, started from March 15th, 2021. IgG and IgM against Receptor Binding Domain (RBD), and IgG against Nucleocapsid protein (N) were measured by chemiluminescence immunoassay (Alinity, Abbott) in the following schedules; before vaccination, and 7, 14, 28 days, 12, 24, 36, 48 weeks after 1st vaccination. A total of 136 vaccinees (including 23 of those with prior infection) were enrolled in this analysis. Single-dose vaccination in participants with prior infection yielded higher IgG (RBD) response than two-dose vaccination in participants without prior infection (mean {+/-} standard deviation, 31,523 {+/-} 14,332 arbitrary units [AU] per mL vs. 22,461 {+/-} 15,661 AU/mL, P = 0.01). IgM (RBD) response was observed in participants without prior infection at 14 days after the first vaccination, achieving a comparable antibody titer compared with those with prior infection (1.41 {+/-} 1.93 chemiluminescence of Sample / Calibrator [S/C] vs. 1.96 {+/-} 2.49 S/C, P = 0.24). IgG (N) showed its specificity and usefulness to differentiate those with and without prior infection, regardless of vaccination. We investigated the participants without prior infection to analyze antibody response according to backgrounds. IgG (RBD) response was significantly lower in those [greater double equals] 40 years old than those < 40 years old (19,087 {+/-} 14,630 AU/mL vs. 25,334 {+/-} 15,849 AU/mL, P = 0.04) at 28 days after 1st vaccination. Low antibody responses were observed in vaccinees with underlying disease or immunosuppressive therapy. Multiple antibody dynamics of vaccinees were clarified in this study. Monitoring each person's antibody titer is warranted in public with expected low and high responders. However, we have yet to observe antibody duration of vaccinees. Therefore, effectiveness of single dose vaccination against those with prior infection is not assessed. Antibody titer follow-up study is in progress.