LAUSR

Abstract Background Rapid decline in antibody-titres after BNT162b2 mRNA COVID-19 vaccine was reported; thus, a booster dose, and recently a second booster were approved. The study aims to discuss immunogenicity throughout the pandemic, especially after booster dose. Methods A prospective study conducted in EMMS-Nazareth hospital, Israel. Anti-SARS-CoV-2 IgG antibody titres were monitored every 5 weeks starting from the vaccine’s second dose. To detect symptomatic and asymptomatic infections, nasopharyngeal swabs for COVID-19 PCR were obtained bi-weekly, and on suggestive symptoms. Third dose of the vaccine was suggested for all participants 5 months after the second one. A comparison was made between those who received three doses (booster-group), and those who were infected after having two doses (infection-group) or three doses (booster-infection) group. Results One-hundred participants were included; 66 finished 14 months of follow-up, out of whom 40 received a third dose, 10 received only two doses—all were infected (mean time for infection 5 ± 12.15 weeks before the designated booster), and 12 received three doses and were infected. The mean titres of these three groups 7 months after the designated booster dose (regardless of receiving it) were 1756 ± 2279; 3483 ± 3016 and 6925 ± 3720 BAU/mL, respectively. The booster group had high titres 7 months after the booster dose, comparable to two months after the second dose (p = .69); The booster-infected group had even higher titres. Conclusion Immunogenicity decline rate after the booster dose is slower than the second dose. Timing of second booster in general population is still to be determined; neutralizing-antibody titres might be helpful.