Explainer | BA.4 and BA.5: what we know about the new Omicron subvariants
- They are now the dominant strains in the US and elsewhere, and many countries are expecting a surge in cases in the coming months
- Studies have shown they can escape antibodies from vaccines and previous infections, but it’s not clear if they cause more severe disease
The new and highly transmissible strains have also gained prevalence elsewhere, including in the United Kingdom and Portugal, and many countries are expecting a surge in cases in the coming months.
Scientists are closely monitoring the new subvariants, with early studies showing that antibodies from existing vaccines and previous Covid-19 infections offer less protection against them. Here’s what we know so far.
Stealthier than ‘stealth Omicron’?
Before BA.4 and BA.5 came along, the prevailing strains in the US were also Omicron subvariants – first BA.2, then BA.2.12.1. Scientists called these earlier subvariants “stealth Omicron” because it was difficult to detect them.
There are different theories about how they evolved – that they came from previous Omicron strains, or are offshoots of BA.2.
While they share similarities with earlier Omicron strains and are seen as close relatives, BA.4 and BA.5 are distinct from them because of mutations in two spike proteins. These mutations make it easier for the two subvariants to escape antibodies produced after Covid-19 vaccines and previous infections caused by other strains – which could be why they have spread so rapidly.