Emergence of SARS-CoV-2 Omicron lineages BA.4 and BA.5 in South Africa

Genomic characterization of the SARS-CoV-2 Omicron lineages BA.4 and BA.5, responsible for the fifth COVID-19 pandemic wave in South Africa, shows continued viral diversification and provides insights into the potential mechanisms underlying the ability of the new lineages to outcompete their predecessors. Three lineages (BA.1, BA.2 and BA.3) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant of concern predominantly drove South Africa's fourth Coronavirus Disease 2019 (COVID-19) wave. We have now identified two new lineages, BA.4 and BA.5, responsible for a fifth wave of infections. The spike proteins of BA.4 and BA.5 are identical, and similar to BA.2 except for the addition of 69-70 deletion (present in the Alpha variant and the BA.1 lineage), L452R (present in the Delta variant), F486V and the wild-type amino acid at Q493. The two lineages differ only outside of the spike region. The 69-70 deletion in spike allows these lineages to be identified by the proxy marker of S-gene target failure, on the background of variants not possessing this feature. BA.4 and BA.5 have rapidly replaced BA.2, reaching more than 50% of sequenced cases in South Africa by the first week of April 2022. Using a multinomial logistic regression model, we estimated growth advantages for BA.4 and BA.5 of 0.08 (95% confidence interval (CI): 0.08-0.09) and 0.10 (95% CI: 0.09-0.11) per day, respectively, over BA.2 in South Africa. The continued discovery of genetically diverse Omicron lineages points to the hypothesis that a discrete reservoir, such as human chronic infections and/or animal hosts, is potentially contributing to further evolution and dispersal of the virus.

Automated summary

The genomic characterization of the SARS-CoV-2 Omicron lineages BA.4 and BA.5, responsible for the fifth wave of the COVID-19 pandemic in South Africa, reveals their continued viral diversification and sheds light on the potential mechanisms that allow these new lineages to outcompete their predecessors. These new lineages, BA.4 and BA.5, share identical spike proteins with BA.2 but have certain differences such as the presence of the 69-70 deletion, L452R, F486V, and the wild-type amino acid at Q493. They can be identified by the S-gene target failure, a proxy marker associated with the 69-70 deletion. BA.4 and BA.5 have rapidly replaced BA.2 and have become the dominant lineages in South Africa.