The fast-spreading Omicron BA.2 variant accounts for nearly 75 percent of US cases

The Omicron COVID subtype BA.2 was detected in 72.2 percent of COVID samples sequenced in the United States, according to the latest estimates from the Centers for Disease Control and Prevention (CDC).

That’s a significant increase from last week’s data, when BA.2 made up an estimated 57.3 percent of the samples — revised upwards from 54.9 percent.

The proportion of BA.2 in US infections has been increasing for weeks, although the actual number of US cases remains relatively low. On April 3, the seven-day moving average of new cases in the US was just over 25,000, down from the peak of over 800,000 in mid-January.

Elsewhere, however, BA.2 has unleashed waves of infection. New cases recently hit record levels in the UK, with around 4.9 million people estimated to have contracted COVID in the week ending March 26, according to the country’s Office for National Statistics (ONS).

Surge cases in the UK

BA.2 has been under investigation for months after scientists noted an increase in the proportion of cases it accounts for since earlier this year. Based on existing data, according to a technical briefing from the UK Health Security Agency (HSA) on March 25, BA.2 is said to have an increased growth rate of about 75 percent compared to the previously dominant BA.1 variant.

At the same briefing, it was noted that there is no evidence of an increased risk of hospitalization after infection with BA.2 compared to BA.1.

A 31 March HSA immunization surveillance report found that vaccine efficacy against both symptomatic disease and hospitalization was similar for BA.1 and BA.2.

A key property of BA.2 is its ability to re-infect people who have already been infected with BA.1. The data shows that a number of people have been infected with BA.2 after BA.1, meaning it is possible to get Omicron twice within a few months.

It remains to be seen whether BA.2 will cause cases to rise in the US in the same way as in the UK, but experts have said it is possible.

When asked if the US would see another such spike in cases, Dr. Ayman El-Mohandes, dean of the City University of New York’s Graduate School of Public Health and Health Policy, told NBC New York: “To be honest, unless we take more precautions and be more responsible, there’s a good chance we will.” we will do that.

“There are already 17 counties across the country that have reached the level where the CDC’s mask mandate is enacted, and of those, three are in New York.”

A COVID testing site seen on March 31, 2022 in Manhattan, New York City. The prevalence of the Omicron BA.2 subtype in the US has increased in recent weeks.
Spencer Platt/Getty

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