Reduced sensitivity of SARS-CoV-2 Omicron variant to booster-enhanced neutralization

The Omicron Variant of Concern (B.1.1.529) has spread internationally and is raising serious concerns about reduced vaccine efficacy and the increased risk of reinfection. We assessed the serum neutralizing activity using a pseudovirus-based neutralization assay in 292 healthcare workers who had received a homologous booster dose of BBIBP-CorV vaccine, 8 to 9 months after completing the priming two-dose vaccination schedule, to investigate whether the newly identified Omicron variant can escape serum antibody neutralization induced by the booster vaccination. The booster dose of BBIBP-CorV rapidly induced a significantly high level of humoral immune response, and the neutralization geometric mean titer (GMT) against the wild-type strain on day 28 after the booster dose was 294.85 (252.99-343.65), 6.1 times higher than the level on day 28 after the second dose. The neutralization against the Omicron variant was also improved by the booster vaccination, although the GMT showed an approximately 20.1-fold reduction to 14.66 (12.30-17.48) when compared with the wild-type strain. This study demonstrated that a booster dose of BBIBP-CorV led to a significant rebound in neutralizing immune response against SARS-CoV-2, while the Omicron variant showed partial resistance to neutralizing antibodies induced by the booster vaccination.