LOS ANGELES - COVID-19 cases are surging again in the United States, powered by a rising tide of Omicron subvariants circulating rapidly across the country.
A new form of the Omicron subvariant, known as BA.2.12.1, has become the dominant strain among new US COVID-19 cases, according to the latest estimates released by the US Centers for Disease Control and Prevention (CDC) on Tuesday.
The new subvariant made up about 58 percent of all new US cases for the week ending May 21, according to the CDC.
The data increased from 49.4 percent a week before, and 39.2 percent two weeks prior, CDC data showed.
BA.2.12.1 spreads more rapidly than previous versions of Omicron. The new version evolved from BA.2, which was more contagious than any previous coronavirus variant.
Yet there was no indication that the new subvariant causes more severe disease than earlier forms did, health experts said.
As Americans approach their Memorial Day weekend, the country is averaging more than 100,000 new confirmed cases per day for the first time since February, according to CDC data.
COVID-19 cases and hospitalizations continued to rise in the country as the death toll from COVID-19 has surpassed one million.
Many regions have moved from low COVID-19 community levels into medium and high levels, according to the CDC.
The country is averaging over 3,000 new COVID-19 hospitalizations each day, up 24.2 percent from a week before, CDC data showed.
The surge came as many of the country's pandemic restrictions were lifted.
Some infectious disease experts said the virus' unpredictable nature could lead to a fickle COVID-19 summer.
Summer surges may hopefully be much less severe this year, because many more people now carry some form of vaccine- or infection-induced immunity, said Dan Barouch, director of the Center for Virology and Vaccine Research at Boston-based Beth Israel Deaconess Medical Center.
Still, it is hard to project exactly what will happen, Barouch said.
Health experts urged the public to wear masks on public transportation and indoor public spaces, even though the country no longer has a federal mask mandate.
The CDC said people who are up to date on vaccines have much lower risk of serious illness and death from COVID-19 compared with people who are unvaccinated.
CDC's COVID Data Tracker showed that in March, adults ages 18 years and older who were unvaccinated were about 5 times more likely to be hospitalized with COVID-19 than those who were up to date.
In the same month, people ages 12 years and older and unvaccinated were 17 times more likely to die of COVID-19 than those who were up to date.