Stealth Omicron BA.2 Now in All U.S. States—Here's What We Know About COVID Sub-Variant

The Omicron BA.2 COVID-19 sub-variant, informally dubbed "Stealth Omicron," has been found in all 50 U.S. states, data shows.

BA.2 is thought to be more contagious than the other Omicron type known as BA.1, which has been, and continues to be for many countries, the dominant version of Omicron.

In Denmark and South Africa, however, BA.2 is the dominant Omicron strain and in other countries its proportion continues to increase.

As of February 25, data from the U.K.'s Health Security Agency (HSA) showed that BA.2 accounted for 30.5 percent of sequenced cases in the country during the previous week. This compares to data from up to January 31, when BA.2 accounted for just 4.1 percent of cases there.

In the U.S., the sub-variant appeared to be less prevalent in recent data, though it has now been found in 49 states in addition to Washington, D.C., according to the variant tracking tool Outbreak.info as of February 25, with the exception of Iowa.

However, a look on the GISAID virus genome database shows that at least one case of BA.2 has indeed been reported from Iowa, taking the state number to 50.

A Centers for Disease Control and Prevention (CDC) estimate of BA.2's presence in the country for the period between February 13 and February 19 suggested it could account for 3.8 percent of cases sequenced in that period. Other Omicron types accounted for the remaining cases in the country.

As BA.2 spreads, scientists have worked to find out more about it. New data has revealed clues as to whether the sub-variant is more likely to leave people hospitalized than BA.1, or whether it is more able to resist vaccines.

According to the U.K. government report out last Friday, preliminary analysis finds no evidence of greater risk of hospitalization with BA.2 when compared to BA.1.

In addition, analysis of vaccine effectiveness continues to show no evidence of reduced effectiveness against symptomatic disease with BA.2 compared to BA.1, the U.K. report stated.

"Two weeks after a booster dose vaccine effectiveness against symptomatic disease with the BA.2 variant was 67 percent," the report added.

Data from Japan had made headlines earlier this month because it suggested that BA.2 could be capable of causing more severe disease based on infected hamsters. However, experts said animal tests are not always relevant to humans.

One key characteristic of BA.2 is its ability to reinfect people who have already had BA.1. Last week, a study emerged documenting dozens of cases from Denmark in which people had caught BA.2 after already having BA.1, meaning they had caught Omicron twice in just a couple of months or so.

However, the researchers said such cases were rare and accounted for just 47 out of more than 1,739 COVID-19 reinfections studied.

Meanwhile, COVID-19 cases in the U.S. continue to fall overall. CDC data shows that the seven-day moving average of new cases was 68,815 on February 25—down from 105,794 a week prior.

COVID test
A stock photo shows someone preparing a lateral flow COVID test. BA.2 continues to spread, though it is more prevalent in some countries than others. Lisa Nentwich/Getty