What are the main differences between the BA.1 subvariant of Omicron and the subvariant BA.2?

Omicron encompasses four main lineages, two of which – BA.1 and BA.2 – have spread worldwide. These subvariants were noticed about the same time in southern Africa but BA.1 was the first to spread across the world. BA.2 has been slowly increasing in frequency over the past few months and in some areas has overtaken BA.1 to become the dominant variant. Both share similar mutations, but they also have additional mutations that make them distinct from one another.

Why has the World Health Organisation recognised BA.2 as a variant of concern?

Much like BA.1, BA.2 is very transmissible and can evade immunity from vaccines and past infections. This makes it a variant of concern.

What has happened in countries where BA.2 has become the dominant Omicron variant?

In Sweden, Denmark, India and other countries, BA.2 has slowly overtaken BA.1 to become the more dominant variant. This means that it has a slight advantage over BA.1, meaning that it is even more contagious. Some early laboratory studies suggested BA.2 could be more severe compared with BA.1 but other studies have since contradicted this – it’s a little too early to tell.

Could we expect to see this variant take over in New Zealand soon, and what would be the possible result if it does?

In New Zealand, we have BA.1 and BA.2 circulating in the community. Routine genomic surveillance performed by ESR, which sequences a proportion of community cases, shows that BA.2 is now about half of the genomes sequenced so the frequency of BA.2 is likely increasing here.  

Could the risk of BA.2 mean we may need public health measures in place for longer? Could it extend the Omicron outbreak?

Because New Zealand is highly vaccinated and boosted, we are in the best possible position to withstand the Omicron wave. Data from Denmark, where about 90 percent of cases are thought to be BA.2, suggest that BA.2 is unlikely to cause a major second wave where BA.1 is already circulating or where booster doses have been rolled out.

Should the public be more worried about this subvariant or treat it with the same precautions as BA.1 in terms of overall risk assessment?

I think it should be treated with the same caution as BA.1. We know that vaccines and boosters provide the best protection against severe disease and dramatically decrease the risk you’ll end up in hospital, and this goes for BA.1 and BA.2.

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