Topline
A close relative of the omicron coronavirus variant—known as BA.2 and dubbed “stealth omicron” by some scientists—is more infectious and better at infecting vaccinated people, a Danish study has found, sparking concerns of an even more transmissible strain as it rapidly outpaces other variants around the world.
The UK is monitoring a sub variant of omicron, BA.2
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Key Facts
People infected with the BA.2 omicron subvariant were around 33% more likely to infect others than those infected with BA.1, the dominant and “original” omicron form, according to an analysis of infections in more than 8,500 Danish households by researchers at Denmark’s Statens Serum Institut (SSI), the University of Copenhagen, Statistics Denmark and the Technical University of Denmark.
The study, which has not yet been peer reviewed, found that those exposed to BA.2 in their household had a 39% chance of getting infected within a week, while the probability for those exposed to BA.1 was 29%.
The BA.2 subvariant was better at infecting vaccinated and booster-vaccinated people than BA.1, the researchers found, though unvaccinated people were still more likely to get infected and transmit the virus.
Omicron BA.2 is “substantially more transmissible than BA.1,” the researchers concluded, adding that the sub-variant has properties that can reduce the protection against infection offered by vaccines.
Early analyses from SSI show no differences in hospitalizations compared to BA.1.
The study is in line with early data from the U.K Health Security Agency (UKHSA), which found BA.2 to have an “increased growth rate” compared to BA.1.
Key Background
While three main sub-lineages of omicron have been described around the world—BA.1, BA.2, and BA.3—BA.1 accounts for almost all cases of omicron. BA.2 is, however, gaining ground in some countries and outcompeting the “original” omicron strain. In Denmark, it quickly overtook BA.1 to become the dominant form, accounting for around a fifth of cases in late 2021, just under half in the second week of January and approximately 82% of cases as of early February. It is also spreading in countries including Britain, France, India and Norway. Despite low case numbers, the UKHSA designated BA.2 a variant under investigation.
What To Watch For
A new variant. While currently grouped under omicron, the genetic difference between BA.1 and BA.2 “is greater than the difference between the original variant and the alpha variant,” the SSI said. Such differences could lead to a distinction in behavior like severity or infectiousness, the SSI noted, but said more work needed to be done to find out. “It is expected that vaccines also have an effect against severe illness upon BA.2 infection,” it added.
What We Don’t Know
A lot. Aside from limited evidence on BA.2’s growth in some regions, there is not a lot of data on its behavior, including whether it is better able to evade immunity, causes more severe illness or how much more transmissible it might be over BA.1. Its genetic makeup may make it harder to spot in some parts of the world, prompting some scientists to give it the nickname “stealth omicron.”
Further Reading
Scientists find ‘stealth’ version of Omicron that may be harder to track (Guardian)
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