Diminished neutralizing activity against the XBB1.5 strain in 55.9% of individuals post 6 months COVID-19 mRNA booster vaccination: insights from a pseudovirus assay on 1,353 participants in the Fukushima vaccination community survey, Japan

Abstract

This study investigates the neutralizing activity against the XBB1.5 variant and the ancestral strain in a population post-bivalent vaccination using a pseudo virus assay validated with authentic virus assay. While bivalent booster vaccination and past infections enhanced neutralization against the XBB 1.5 strain, individuals with comorbidities showed reduced responses. The study suggests the need for continuous vaccine updates to address emerging SARS-CoV-2 variants and highlights the importance of monitoring real-world immune responses.

Keywords: SARS-CoV2; antibody waning; bivalent vaccination; mRNA vaccination vulnerable population; vaccination.

Figure 1

Neutralizing responses against the Wuhan strain and XBB1.5 strain. (A) distribution of neutralizing responses in the entire cohort, (B) comparative distribution of neutralizing responses: naive vs. previously infected, (C) distribution of neutralizing responses relative to time elapsed since last vaccination, months; M, (D) age-stratified distribution of neutralizing responses, years old; y.o., (E) vaccine type-specific distribution of neutralizing responses and (F) distribution of neutralizing responses by number of vaccine doses administered. 126 participants (9.3%) received three doses of an ancestral-strain monovalent vaccine (V3 group). 467 (37.5%) received three doses of a monovalent vaccine and one dose of a bivalent vaccine (V3+Bi group), 56 (4.1%) were administered four doses of the monovalent vaccine (V4 group), and 704 (52.0%) received four doses of a monovalent vaccine and one dose of a bivalent vaccine (V4+Bi group). *; p<0.05, **; p<0.01, ***; p<0.001.