(NewsNation) — Omicron sub-variant BA.2 was estimated to represent almost a quarter of all variants circulating in the U.S. as of March 12, the U.S. Centers for Disease Control and Prevention said on Tuesday.

BA.2 has been tracked by scientists as the subvariant spreads rapidly in parts of Asia and Europe. In the U.S., it makes up 23.1% of coronavirus variants in circulation.

Five lineages are designated as omicron variants: B.1.1.529, BA.1, BA.1.1, BA.2, and BA.3.

Currently, there are 79,418,377 COVID-19 cases in the U.S. being reported by the CDC. Daily cases in the country have started to decline, and as a result, Coronavirus restrictions in many areas have lessened greatly.

Recently, the U.S. government said it will run out of COVID-19 treatment supplies known as monoclonal antibodies as soon as late May, and plans to scale back attempts to get more unless Congress provides more funding.

Although authorities have said vaccinations offer strong protection against severe illness from COVID-19, they haven’t help up as well against milder infections due to omicron. During the omicron wave, effectiveness against hospitalization was 91% in people who had gotten their booster two months earlier.

On Tuesday, Pfizer and its partner BioNTech asked regulators to authorize an additional booster dose of its COVID-19 vaccine for seniors. So far, a fourth dose has only been recommended for people with severely weakened immune systems in the U.S.

Reuters and the Associated Press contributed to this story.