Dynamics of antibody responses, cellular immunity, and breakthrough infections among Japanese healthcare workers during the 6 months after receiving two doses of BNT162b2 mRNA vaccine

Introduction

The waning of the antibody titre after the first two doses of the Pfizer-BioNTech BNT162b2 mRNA SARS-CoV-2 vaccine was reported. However, knowledge of the dynamics of cellular immunity is scarce. Here, we performed a prospective cohort study to disclose antibody and cellular immunity dynamics and discuss the relationship between immunity and breakthrough infection.

Methods

The study had a prospective cohort design. Antibody titres against SARS-CoV-2 in serially collected serum samples of 608 Japanese vaccinees after 6 months of vaccination were measured. Simultaneously, T-cell immunity dynamics were assessed using the QuantiFERON SARS-CoV-2 assay. Additionally, participants with suspected breakthrough infection were detected according to the positive conversion of the IgG assay for nucleocapsid proteins of SARS-CoV-2.

Results

Antibody titres were elevated 3 weeks after vaccination and waned over the remainder of the study period. The QuantiFERON SARS-CoV-2 assay performed on 536 participants demonstrated the similar dynamics. Six participants without predisposing medical conditions demonstrated positive conversion of the IgG assay for nucleocapsid proteins, while five were asymptomatic.

Conclusion

Waning of humoral and cellular immunity within 6 months of administration of two doses of BNT162b2 vaccine among Japanese healthcare professionals and the occurrence of asymptomatic breakthrough infection was suspected in approximately 1 of 100 vaccinees.

(UMIN000043340)