A substrain of omicron is responsible for a growing number of infections.
BA.2.12.1, a subvariant of the COVID-19 Omicron strain, is now the cause of approximately 1 in 5 infections in the United States. Most U.S. infections are still linked to BA.2, the parent strain, which is responsible for 75% of domestic outbreaks.
"SARS-CoV-2, the virus that causes COVID-19, is constantly changing and accumulating mutations in its genetic code over time," the CDC warned in a recent report. "New variants of SARS-CoV-2 are expected to continue to emerge. Some variants will emerge and disappear, while others will emerge and continue to spread and may replace previous variants."
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The U.S. has seen a major deescalation of COVID-19 regulation as the rate of vaccination has increased and the amount of deaths caused by the novel disease has steadily fallen.
The Biden administration has been leaning on Congress to approve additional pandemic relief funding, saying money for fourth COVID-19 vaccine shots is gone.
Dr. Ashish Jha, the new White House coronavirus response coordinator, told "CBS Mornings" on Monday that if the coronavirus situation in America becomes "substantially worse," U.S. health officials could return to looking at things like masking.
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The U.K. Health Security Agency said last week that work was underway to "precisely define the phylogeny" of the new variants BA.4 and BA.5.
In an April 8 update, the organization wrote that BA.4 had been found in South Africa, Denmark, Botswana, England and Scotland.
All BA.5 cases were in South Africa, but Botswana's ministry of health reportedly said it had identified four cases of both BA.4 and BA.5 among individuals aged 30 to 50 years old who were fully vaccinated and experiencing mild symptoms.
Fox News's Julia Musto contributed to this report.