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BA.2 ‘Stealth’ Variant Found in Nearly All U.S. States as Reinfection Capability Unclear

The Omicron subvariant known as BA.2, or unofficially as “stealth Omicron,” has now been found in the vast majority of U.S. states, data shows.

The subvariant has made headlines this year after being behind an increasingly high proportion of cases in countries such as Denmark—where most new COVID cases are now BA.2—and the U.K.

The variant has also been found to a lesser extent in the U.S., where according to the variant tracking tool as of Monday, it had been reported in 47 states. uses data submitted to the virus genome database GISAID.

Despite BA.2 being found widely across the U.S., it doesn’t appear to account for many cases. shows it has been found in just 790 sequenced cases, whereas Omicron as a whole has accounted for more than 370,000 in the country.

Data from the U.S. Centers for Disease Control and Prevention (CDC) showed on Monday that BA.2 accounted for 3.6 percent of all COVID cases in the country between January 30 and February 5, with other Omicron subtypes accounting for the remaining 96.4 percent.

Data from some countries has shown that BA.2 has a faster growth rate compared to the BA.1 Omicron subtype, which has been responsible for most Omicron cases. However, other aspects of the variant are yet to be conclusively determined.

Dr. Troels Lillebaek, chairman of the Danish SARS-CoV-2 Variant Assessment Committee, told Newsweek last week that so far, no difference in hospitalization risk has been found in BA.2 compared to BA.1, based on limited data.

In addition, vaccines appear to work as well against BA.2 as they do against BA.1, according to data from the U.K.’s Health Security Agency (HSA) that was published in a technical briefing on February 11. It stated that sera—blood, essentially—from people with recent booster shots was able to neutralize both variants similarly. It’s unclear if this will change over time.

Reinfection Risk

One of the most significant unknowns about BA.2 is whether it can reinfect people who have already caught BA.1, meaning people could potentially catch COVID twice in just a couple of months.

The HSA evaluated this for its February 11 report and found that there has been “no detected sequence-confirmed BA.2 reinfection following a BA.1 infection at any interval to date in England.”

The same question was brought up in a World Health Organization (WHO) question-and-answer session last Tuesday, and Dr. Abdi Mahamud, the organization’s incident manager, said the answer was unclear.

“Right now the main question [is] if I got BA.1, can I get BA.2… we don’t know. We haven’t had time,” Mahamud said. “For WHO, we use 90 days between the two infections, so we are still just starting the period.”

BA.2 may be referred to by some as “stealth Omicron” since it shows up differently on COVID tests than the existing dominant Omicron type.