Blended BA.5 infection within 8 days after a boosted bivalent mRNA vaccination strengthens and lengthens the host immunity

The impact of SARS-CoV-2 infection shortly after vaccination on vaccine-induced immunity is unknown, which is also one of the concerns for some vaccinees during the pandemic. Here, based on a cohort of individuals who encountered BA.5 infection within 8 days after receiving the fourth dose of a bivalent mRNA vaccine, preceded by three doses of inactivated vaccines, we show that booster mRNA vaccination provided 48% protection efficacy against symptomatic infections. At Day 7 postvaccination, the level of neutralizing antibodies (Nabs) against WT and BA.5 strains in the uninfected group trended higher than those in the symptomatic infection group. Moreover, there were greater variations in Nabs levels and a significant decrease in virus-specific CD4+ T cell response observed in the symptomatic infection group. However, symptomatic BA.5 infection significantly increased Nab levels against XBB.1.9.1 and BA.5 (symptomatic > asymptomatic > uninfected group) at Day 10 and resulted in a more gradual decrease in Nabs against BA.5 compared to the uninfected group at Day 90. Our data suggest that BA.5 infection might hinder the early generation of Nabs and the recall of the CD4+ T cell response but strengthens the Nab and virus-specific T cell response in the later phase. Our data confirmed that infection can enhance host immunity regardless of the short interval between vaccination and infection and alleviate concerns about infections shortly after vaccination, which provides valuable guidance for developing future vaccine administration strategies.

Immune escape of BA.2.86 is comparable to XBB subvariants from the plasma of BA.5- and BA.5-XBB-convalescent subpopulations

The EG.5.1 variant of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has been prevalent since mid-July 2023 in the United States and China. The variant BA.2.86 has become a major concern because it is 34 mutations away from the parental variant BA.2 and >30 mutations from XBB.1.5. There is an urgent need to evaluate whether the immunity of the population and current vaccines are protective against EG.5.1 and BA.2.86. Based on a cohort of two breakthrough-infected groups, the levels of neutralizing antibodies (NAbs) against different subvariants were measured using pseudovirus-based neutralization assays. XBB.1.5, EG.5.1, and BA.2.86 are comparably immune-evasive from neutralization by the plasma of individuals recovered from BA.5 infection (BA.5-convalescent) or XBB.1.9.2/XBB.1.5 infection following BA.5 infection (BA.5-XBB-convalescent). NAb levels against EG.5.1 and BA.2.86 subvariants remained >120 geometric mean titers (GMTs) in BA.5-XBB-convalescent individuals 2 months postinfection but were <40 GMTs in BA.5-convalescent individuals. Furthermore, the XBB-targeting messenger RNA (mRNA) vaccine RQ3033 induced higher levels of NAbs against XBB.1.5, EG.5.1, and BA.2.86 than against BA.5-XBB infection. The results suggest that BA.2.86 and EG.5.1 are unlikely to cause more severe concerns than the currently circulating XBB subvariants and that the XBB.1.5-targeting mRNA vaccine tested has promising protection against EG.5.1 and BA.2.86.