Dynamics of anti-Spike IgG antibody titer after the third BNT162b2 COVID-19 vaccination in the Japanese health care workers

Introduction

Many countries are administering a third dose of some coronavirus disease 2019 (COVID-19) vaccines, but the evaluation of vaccine-induced immunity is insufficient. This study aimed to evaluate anti-spike immunoglobulin G (IgG) titers in the health care workers after the third BNT162b2 vaccination.

Methods

Dynamics of anti-spike IgG titers were assessed two months following the third BNT162b2 vaccination in 52 participants. All participants received the primary series of vaccination with BNT162b2 and received the third dose eight months after the second vaccination. Associations between anti-spike IgG titer, baseline characteristics, and adverse reactions were also evaluated.

Results

The geometric mean titer of anti-spike IgG one month after the third vaccination was 17400 AU/ml, which increased to approximately 30 times immediately before the third vaccination and approximately twice that one month after the second vaccination. In addition, participants with anti-spike IgG titers less than 10000 AU/ml after the second vaccination tended to have higher increases in ant-spike IgG titers before and after the third vaccination.

The decline rate of anti-spike IgG was significantly slower after the third vaccination as 35.7% than that after the second vaccination as 59.1%. The anti-spike IgG titer was significantly negatively associated with age ( r = -0.31). Participants who had a headache at the vaccination showed significantly higher anti-spike IgG titer than those without a headache.

Conclusions

The anti-spike IgG induced by primary immunization with BNT162b2 waned over time. The third dose of BNT162b2 substantially increased the anti-spike IgG with a slower decline rate.