Second monovalent SARS-CoV-2 mRNA booster restores Omicron-specific neutralizing activity in both nursing home residents and health care workers.

We examined whether the second monovalent SARS-CoV-2 mRNA booster increased antibody levels and their neutralizing activity to Omicron variants in nursing home residents (NH) residents and healthcare workers (HCW). We sampled 367 NH residents and 60 HCW after primary mRNA vaccination, first and second boosters, for antibody response and pseudovirus neutralization assay against SARS-CoV-2 wild-type (WT) (Wuhan-Hu-1) strain and Omicron BA1 variant. Antibody levels and neutralizing activity progressively increased with each booster but subsequently waned over weeks. NH residents, both those without and with prior infection, had a robust geometric mean fold rise (GMFR) of 10.2 (95% CI 5.1, 20.3) and 6.5 (95% CI 4.5, 9.3) respectively in Omicron-BA.1 subvariant specific neutralizing antibody levels following the second booster vaccination (p<0.001). These results support the ongoing efforts to ensure that both NH residents and HCW are up to date on recommended SARS-CoV-2 vaccine booster doses.