ABSTRACT
Since China eased its COVID-19 response strategies in late 2022, we have been witnessing a rapid and wide spread of SARS-CoV-2 infection across the major cities, including capital Beijing, where Omicron subvariant BF.7 has been dominating the infection. Here, we show that such expansion is unlikely due to a higher binding affinity of BF.7 to human receptor angiotensin-converting enzyme 2 (ACE2) as the similar binding activities were found for other Omicron subvariants tested such as BA.1, BA.5.2, BQ.1, BQ.1.1, XBB, and XBB.1. Additionally, through study of antibody response among six different clinical cohorts, we found that primary infection with BF.7 among the unvaccinated individuals only elicited type-specific neutralizing antibodies to the infecting virus and its close related strains. By a distinct contrast, breakthrough infection with BF.7 among the vaccinated individuals, particularly those severe cases, induced strong and broadly neutralizing antibodies to a diverse panel of SARS-CoV-2 variants and Omicron subvariants including the XBB lineage. A deeper understanding of how these broadly neutralizing antibodies were generated or boosted by BF.7 breakthrough infection will hold the key for augmenting antibody immunity against diverse SARS-CoV-2 variants.