Abstract
While mRNA vaccines against SARS-CoV-2 are exceedingly effective in preventing symptomatic infection, their immune response features remain to be clarified. In the present prospective study, 225 healthy individuals in Japan, who received two BNT162b2 doses, were enrolled. Correlates of BNT162b2-elicited SARS-CoV-2-neutralizing activity (50% neutralization titer: NT50; assessed using infectious virions) with various determinants were examined and the potency of sera against variants of concerns was determined. Significant rise in NT50s was seen in sera on day 28 post-1st dose. A moderate inverse correlation was seen between NT50s and ages, but no correlation seen between NT50s and adverse effects. NT50s and SARS-CoV-2-S1-binding-IgG levels on day 28 post-1st dose and pain scores following the 2nd dose were greater in women than in men. The average half-life of NT50s was ~ 68 days, and 23.6% (49 out of 208 individuals) failed to show detectable neutralizing activity on day 150. While sera from elite-responders (NT50s > 1,500: the top 4% among the participants) potently to moderately blocked all variants of concerns examined, some sera with low NT50s failed to block the B.1.351-beta strain. Since BNT162b2-elicited immunity against SARS-CoV-2 is short, an additional vaccine or other protective measures are needed.
Highlights
While mRNA vaccines against SARS-CoV-2 are exceedingly effective in preventing symptomatic infection, their immune response features remain to be clarified
We first determined the neutralizing activity against SARS-CoV-2 in sera samples taken on day 7 post-1st dose from 225 participants; none of the samples showed detectable neutralization activity (NT50 < 20)
There was a high positive correlation of the N T50 values with S1-binding-IgG levels (Spearman’s ρ = 0.71; 95% CI 0.63–0.77, p < 0.001) as examined on day 28 post-1st dose, while there was a moderate positive correlation of the N T50 values with S1-binding-IgM levels (Spearman’s ρ = 0.43; 95% CI 0.31–0.53, p < 0.001), suggesting that the neutralizing activity largely resides in IgG fraction of the sera of vaccinated participants around on day 28 post-1st dose (Fig. 1B, C)
Summary
While mRNA vaccines against SARS-CoV-2 are exceedingly effective in preventing symptomatic infection, their immune response features remain to be clarified. A phase 2b trial in South Africa showed 60% efficacy, in which approximately 90% of the endpoints occurred in subjects infected with the beta v ariant[19,20], suggesting that the beta variant is less susceptible to antibodies elicited with the original Wuhan strain antigens, which is in the composition of all the vaccines currently being e valuated[7]. Another recent concern is the emergence of a B.1.617.2 (delta) variant, which was first detected in India, is spreading around the world. Decline of BNT162b2-elicited immune response and activity of the elite and moderate responders against VOCs were investigated
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