Serum neutralisation of the SARS-CoV-2 omicron sublineage BA.2

The rapidly emerging SARS-CoV-2 omicron variant is associated with high transmissibility, compromised serum neutralising activity, and reduced vaccine effectiveness.1–3 BA.1 is the dominant omicron sublineage, making up more than 97% of omicron variant sequences worldwide in November and December, 2021, whereas BA.2 and BA.3 were rare.3 Hence, early studies of the omicron variant were mainly based on the BA.1 sublineage. Since early January, 2022, there has been a sudden upsurge of BA.2 in Europe and Asia, accounting for 15·6% of omicron variant sequences detected at the end of January, 2022.