As this SARSCoV2 evolutionary tree suggests, the BA.1 and BA.2 strains of the Omicron variant are about as genetically distinct as earlier variants Alpha, Beta, and Gamma are from each other. Learn more: ScienceVisuals
from Denmark posted this week as a preprint make it clear BA.2 is inherently more transmissible than BA.1, leaving scientists to wonder which of its distinct mutations confer an advantage.
Although BA.2 represented less than 4% of all Omicron sequences in the leading global virus database as of 30 January, it has been identified in 57 countries, with the earliest documented case dating to 17 November in South Africa. It likely now dominates in India, according to Bijaya Dhakal, a molecular biologist at the Sonic Reference Laboratory in Austin, Texas, who examined sequence data uploaded from eight large Indian states. In the United Kingdom, the proportion of likely BA.
The study from Denmark, which sequences the virus from virtually every person who gets COVID-19, paints a more dramatic picture. In households where the first case was BA.1, on average 29% of other people in the household became infected. When the first case was BA.2, 39% of household members were infected.
Much as scientists a few weeks ago wondered whether a previous infection with Delta or another variant would protect people from Omicron overall, some are now looking for data on whether Omicron’s first surge created a shield against BA.2. “To what extent does a BA.1 infection protect you against reinfection with BA.2?” Zeller asks. “From what I have seen in Denmark, it’s not going to be 100%.”