As Stealth Omicron BA.2 COVID Variant Found in 30 States, Here's What We Know

The Omicron COVID sub-variant BA.2 has been detected in more than half of U.S. states as it continues to spread across dozens of countries.

BA.2 has become a major focus after rising rapidly in certain countries, particularly Denmark, where it now accounts for the vast majority of new cases and has outcompeted the previous Omicron sub-type BA.1, which has been the most common type worldwide, according to the World Health Organization (WHO).

As of February 1, BA.2 had been found in just over 200 U.S. COVID cases from at least 30 states, according to, a variant tracking tool that uses data from the virus genetic database GISAID. BA.2 had also been found in about 57 countries. These figures may of course change rapidly.

On January 28, Trevor Bedford, a biostatistics professor at the Fred Hutch disease research center, tweeted that BA.2 had "become predominant in Denmark and India" and was spreading elsewhere.

He added that its frequency was estimated to be around 82 percent in Denmark, 9 percent in the U.K. and 8 percent in the U.S.

Part of the concern surrounding BA.2 is that it appears to be more transmissible than the BA.1 subtype.

On Monday, researchers from Denmark's Statens Serum Institut, an infectious disease research organization, released a pre-print study that looked at the transmission dynamics of BA.2 and BA.1 and concluded that there was a higher chance of being infected with BA.2 following household exposure than BA.1. It should be noted that the study is a pre-print and hasn't been subjected to the rigorous scientific criticism of the peer review process.

The researchers looked at COVID case data from more than 8,500 Danish households and observed the secondary attack rate (SAR), defined as the probability that an infection occurs among susceptible people in a specific group.

The SAR was estimated at 29 percent in households with BA.1 and 39 percent in households infected with BA.2. The study also suggested that BA.2 is more able to dodge vaccines than BA.1, based on the household data.

However, the study also found that the pattern of increased transmissibility in BA.2 households wasn't observed for fully vaccinated and booster-vaccinated primary cases.

In other words, the researchers concluded that BA.2 is "inherently substantially more transmissible than BA.1," but that its immune-evasion properties "do not increase its transmissibility from vaccinated individuals with breakthrough infections."

The study was published in the medRxiv pre-print database on January 30.

Last week, data from the U.K. suggested that vaccine effectiveness against symptomatic disease was similar for BA.1 and BA.2.

Health worker
Health workers carry out COVID tests at a testing site in Nootdorp, Netherlands, on January 25, 2022. Patrick van Katwijk/Getty