BA.2, the omicron sub-variant, now accounts for nearly 35% of all COVID-19 variants in the U.S., according to the Centers for Disease Control and Prevention (CDC). 

The agency's data shows BA.1.1 makes up 57.3%.

B.1.1.529, or the original omicron, accounts for 7.9%

OMICRON SUBVARIANT BA.2: HEALTH OFFICIALS CALL IT 'VARIANT OF CONCERN'

BA.2 has been classified as a "variant of concern" by the CDC and the World Health Organization (WHO)

The CDC previously estimated that BA.2 made up 22.3% of circulating variants in the country for the week ending on March 12. 

WHO officials have warned that studies on BA.2 have shown it has a growth advantage over BA.1 and "appears inherently more transmissible." 

FILE - Commuters wear face masks and social distance while riding an M Train, Tuesday, March 9, 2021, in New York's subway system.

FILE - Commuters wear face masks and social distance while riding an M Train, Tuesday, March 9, 2021, in New York's subway system. (AP Photo/Mary Altaffer, File)

Studies are being conducted to evaluate the risk of reinfection with BA.2 compared with BA.1. Reinfection with BA.2 following infection with BA.1 has been documented, though initial data suggests infection with BA.1 provides strong protection against reinfection with BA.2 for a limited period.

The WHO says it will continue to closely monitor BA.2., including whether it causes more severe disease. 

BA.2, which has a lot of mutations can appear like a delta infection because it lacks a genetic quirk of the original omicron variant.

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Vaccines appear to be just as effective against the sub-variant, according to early research. 

BA.2 has been found in more than 80 countries, as well as across all 50 U.S. states. 

While COVID-19 cases have fallen markedly since the winter's surge, a coronavirus resurgence in Asia and Europe sparked by the BA.2 sub-variant has raised questions about America's pandemic future. 

Scientists have warned about the possibility of new variants throwing a wrench in plans to return to "normal," although face mask and vaccine restrictions and regulations have already been lifted nationwide.

"In terms of early studies, we have not seen any studies that suggest it’s more severe, nor have we seen studies that suggests that it will evade our vaccines any more so than omicron has already – and, in fact, that our vaccines will work just like it has with omicron," CDC Director Dr. Rochelle Walensky said at a February White House COVID-19 response team briefing.

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However, while omicron variants are milder than delta, a CDC study shows that they're three to five times deadlier than pre-delta variants. 

Notably, it is difficult for researchers to predict how much BA.2 will change caseloads because it is spreading in communities with varying levels of protection from vaccines and prior infections. 

The Associated Press contributed to this report.