More contagious omicron BA.2 subvariant now dominant in the U.S., CDC says

The more contagious omicron subvariant, BA.2, is now the dominant version of Covid-19 in the U.S., according to data released by the Centers for Disease Control and Prevention this week.

The subvariant accounts for nearly 55% of Covid infection samples that have undergone genetic sequencing. Even so, the spread of a more contagious strain does not guarantee the U.S. will endure a new wave of cases.

BA.2 has doubled as a proportion of circulating variants of the virus in the U.S. about every two weeks. At the beginning of February, the omicron subvariant made up just 1% of sequenced Covid cases in the U.S.

The BA.2 subvariant spreads about 75% faster than the earlier version of omicron, BA.1, according to the latest update from the U.K. Health Security Agency. BA.2 has caused a spike in infections in the U.K. and Germany in recent weeks, though cases have started to decline again there.

China has been battling its worst outbreak since 2020, which is also driven by BA.2

Though BA.2 spreads faster, it does not make people sicker than the earlier version of omicron, according to data from South Africa and the U.K., among other countries. Omicron and its subvariants generally result in less severe illness than the delta variant. Scientists in Qatar have found that Covid vaccines are as effective against BA.2 as they were against BA.1, though omicron has caused more breakthrough infections.

White House chief medical advisor Dr. Anthony Fauci said earlier this month that BA.2 could cause an uptick in cases in the U.S. But he does not expect another surge. Fauci said the country does not yet need to reintroduce Covid restrictions in response to the subvariant.

In New England, BA.2 now makes up about 73% of all Covid cases that have undergone genetic sequencing, according to the CDC. In New York and New Jersey, BA.2 represents more than 70% of sequenced cases. Throughout the pandemic, the Northeast has often been an epicenter of new variants and a harbinger of what the rest of the nation will face.

New infections have plummeted 96% since the peak of the unprecedented wave of omicron cases in January, according to a CNBC analysis of data from Johns Hopkins University. Hospital admissions from Covid have plunged 92% from the peak of the winter spike, according to data from the CDC.

The CDC has shifted its focus to hospitalizations, an indicator of how much severe illness the virus is causing, when issuing public health guidance on Covid. Earlier this month, the CDC said 98% of the U.S. population lives in areas where they can go without face masks.

Ali Mokdad, a leading epidemiologist at the Institute for Health Metrics and Evaluation at the University of Washington, said Covid cases will continue to decline through the spring and summer due to built up immunity from vaccines and the winter omicron wave. Mokdad said another surge is possible in the winter as protection from the vaccines wanes.

However, Michael Osterholm — a top epidemiologist at the Center for Infectious Disease Research and Policy at the University of Minnesota — said it is unclear how BA.2 will affect the U.S. It is difficult to predict what the variant's spread in one country means for another nation, because previous strains have affected parts of the world differently, he added.

Osterholm said the U.S. has had high levels of immunity before, only to see a major surge. In December, about 95% of the U.S. population ages 16 and older had antibodies against the virus either through vaccination or infection, according to a CDC survey of blood donor samples.

However, omicron still managed to cause the most infections of the entire pandemic weeks later.