The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.1.529 (omicron) variant has three major sublineages: BA.1, BA.2, and BA.3.1 BA.1 rapidly became dominant and has shown substantial escape from neutralizing antibodies induced by vaccination.2-4 The number of cases of BA.2 has recently increased in many regions of the world, suggesting that BA.2 has a selective advantage over BA.1. BA.1 and BA.2 share multiple common mutations, but each also has unique mutations1 (Figure 1A). The ability of BA.2 to evade neutralizing antibodies induced by vaccination or infection is unclear.
We evaluated neutralizing antibody responses against the parental WA1/2020 strain of the virus, as well as against the omicron BA.1 and BA.2 variants, in 24 persons who had been vaccinated and boosted with the BNT162b2 mRNA vaccine (Pfizer–BioNTech)5 and had not had infection with SARS-CoV-2 and in 8 persons with a history of SARS-CoV-2 infection, irrespective of vaccination status. Demographic and clinical characteristics of the study population are provided in Tables S1 and S2 in the Supplementary Appendix, available with the full text of this letter at NEJM.org.