There are already dozens of cases in almost half of the United States of a new Covid subvariant that is even more contagious than the already highly transmissible omicron variant.
Nearly half of U.S. states have confirmed the presence of BA.2 with at least 127 known cases nationwide as of Friday, according to a global database tracking Covid variants. The Centers for Disease Control and Prevention said in a statement Friday that although BA.2 has increased relative to the original omicron strain in some countries, it is currently circulating at a low level in the United States.
The subvariant is 1.5 times more transmissible than the original omicron strain, by researchers referred to as BA.1, according to the Statens Serum Institut, which performs infectious disease surveillance for Denmark.
The new pedigree does not appear to further reduce the effectiveness of vaccines against symptomatic infection, according to the UK Health Security Agency.
"Currently, there is no evidence that the BA.2 genus is more serious than the BA.1 genus," said CDC spokeswoman Kristen Nordlund.
BA.2 overtook the original omicron as the dominant variant in Denmark within a few weeks, says Troels Lillebæk, chairman of the Scandinavian nation's committee, which monitors Covid variants.
BA.1 and BA.2 have many differences in their mutations in the main areas. In fact, the difference between BA.1 and BA.2 is greater than the difference between the original "wild strain" and the Alpha variant, which was the first major mutation to take root worldwide.
The BA.2 variant has five unique mutations on a key part of the tip protein, which the virus uses to bind to human cells and invade them, Lillebæk told CNBC. Mutations on this part of the tip, known as the receptor binding domain, are often associated with higher transmissibility.
The UK Health Security Agency said on Friday that BA.2 has a "significant" growth advantage over the original omicron. The sister variant spread faster than the original omicron in all regions of England, where there were enough cases to conduct an analysis, according to the agency.
However, a preliminary assessment found that BA.2 does not appear to reduce the efficacy of vaccines more than the original omicron. A booster dose was 70% effective in preventing symptomatic disease from BA.2 two weeks after receiving the shot compared to 63% efficacy for the original omicron strain.
The World Health Organization has not labeled BA.2 as a variant of concern. However, WHO officials have repeatedly warned that new variants will emerge as omicron spreads around the world at an unprecedented rate. Maria Van Kerkhove, WHO's Covid-19 technical director, warned on Tuesday that the next Covid variant would be more transferable.
"The next variant of concern will be more appropriate, and what we mean by that is that it will be more transferable because it will have to overtake what is currently circulating," Van Kerkhove said. "The big question is whether future variants will be more or less severe."
Lillebæk said that there is not yet enough data to determine whether BA.2 is capable of re-infecting people who captured the original omicron. However, previous infection is likely to confer some crossover immunity to BA.2.
Pfizer and Moderna started clinical trials this week with omicron-specific shots amid growing concern that new variants will emerge as the immunity induced by the original vaccines diminishes.
New Covid cases are on the rise in Denmark, with more than 50,000 new infections reported Friday in a country of 5.8 million people, according to the country's Ministry of Health. Lillebæk said that it is safe to assume that BA.2 is driving the increase in the number of new infections in Denmark right now.
New hospital admissions in Denmark increased by 12 for a total of 967 patients who are covid-positive. Lillebæk said that this increase is probably within the limits of what the health system can handle. He noted, however, that 80% of Danes are fully vaccinated, and 60% have received booster injections.
"If you are in a community or live in a country where you have a low vaccination rate, then you will definitely have more hospital admissions and more serious cases and then more in the intensive care unit," he said.
In the United States, about 67% of those eligible are fully vaccinated, according to CDC data.