The Omicron variant sub-lineage BA.2 now makes up a majority of new infections in the United States, the Centers for Disease Control and Prevention estimated Tuesday.
Last week, 54.9% of cases were caused by the strain nationwide. BA.2's prevalence remains highest in the Northeast, where the agency estimates that the variant made up close to three in four new infections in the region spanning New Jersey through Maine.
Federal health officials say the faster-spreading strain has not yet led to the steep climb in cases reported in many countries abroad, or many more severe cases compared to the otherstrains, despite in the United States for months.
However, its rising prevalence has raised concern in Northeast communities now seeing early signs of an uptick in cases — and has forced authorities to end the use of at least one key COVID-19 treatment, a monoclonal antibody drug that isn't effective against BA.2.
"This small increase in cases in the Northeast is something that we are watching very closely as we look for any indication of an increase in severe disease from COVID-19 and track whether this might represent an increase in the strain that's being put on hospitals," the CDC's Dr. John Brooks told an event hosted by Ethnic Media Services on Friday.
Brooks acknowledged the "warning signal" seen in the agency's wastewater surveillance from the Northeast, which samples sewage in hundreds of sites searching for early signs of a surge. Nationwide, around half of sites are seeing an increase.
However, Brooks and other federal health officials have speculated BA.2's spread was likely on track to lead to simply small regional increases in cases as opposed to a new surge — thanks in part to the sharp national spike in Omicron cases that occurred over the winter.
The overall pace of new cases has hovered around 27,000 reported daily for more than a week. The cadence of new hospital admissions is also continuing to fall nationwide, down more than 90% from the Omicron wave's peak.
"There are greater than 95% of Americans who have some evidence of either having been vaccinated or previously infected with COVID. We think that's very high compared to some other places in the world," said Brooks.
The agency's variant estimates rely largely on sampling test data from laboratories, officials acknowledge, and will not pick up on cases only spotted by the growing number of Americans relying on at-home rapid tests to see if they are infected.
However, a CDC spokesperson said that the agency remains confident that there have been enough positive lab tests "available for sequencing purposes" and that the agency's "Nowcast" estimates account for "changes in testing by design."
"CDC and state and local public health agencies rely on multiple types of data sources to maintain a complete picture of disease impact, including monitoring of BA.2," Jasmine Reed, the spokesperson, said in a statement.
Based also on the agency's state-level estimates, which lag by a month because of the time needed to accumulate enough sequences, the Food and Drug Administration announced on Friday it was ending use in the Northeast of sotrovimab.
The drug, produced by GlaxoSmithKline and Vir Biotechnology, is one of the last two remaining monoclonal antibody drugs that were effective at treating Omicron cases. The companies say they plan to ask the FDA to greenlight a higher dose of the drug for BA.2 cases.
In addition to the antiviral pills from Pfizer and Merck, the FDA has also authorized Eli Lilly's monoclonal antibody bebtelovimab to treat Omicron cases. However, a panel of top doctors convened by the National Institutes of Health said earlier this month doctors should use that drug as a last resort to treat COVID-19 cases only if better-supported options were not available.
Around 30,000 courses of sotrovimab and of bebtelovimab were allocated to states and territories this week by the Biden administration. By comparison, there are more than 175,000 courses of Pfizer's Paxlovid pills also being made available — though officials have cautioned supply will dry up if their COVID-19 funding request remains stalled on Capitol Hill.
"Our current supply of monoclonal antibody treatments is projected to run out as soon as late May of this year. Last Monday, we had to cut the supply of monoclonal antibody treatments," Health and Human Services Secretary Xavier Becerra told reporters this week.
"We will do what we can with what we have, and we will continue to work with Congress to secure more of those funds that we need," said Becerra.
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