The Omicron subvariants, known as BA.4 and BA.5, continue their rapid march across the United States and together have become dominant among new coronavirus cases, according to new estimates on Tuesday from the Centers for Disease Control and Prevention.
As of the week ending Saturday, BA.4 made up 15.7 percent of new cases, and BA.5 accounted for 36.6 percent, accounting for about 52 percent of new cases in the United States, figures experts say. should rise in the coming weeks .
The statistics, released Tuesday morning, are based on modeling and may be revised as more data comes in, which happened in late December when the agency’s estimates missed the mark.
The release came the day that independent advisers to the Food and Drug Administration met Tuesday to consider updating vaccines with a booster shot for Americans that could better match some versions of Omicron, even though the virus could return by the fall. can evolve.
In the less than six months since BA.4 and BA.5 were first detected in South Africa, the two subvariants in the United States appeared to overtake two previous Omicron subvariants, including BA.2, which for a time was the predominant version was earlier this spring. The other, BA.2.12.1, was dominant only as of the week ending June 18, according to CDC estimates. After Omicron arrived in the United States, it caused the number of cases to skyrocket during the winter. Before that, the Delta variant had been dominant in the United States since early summer.
BA.4 and BA.5 exhibit the qualities of escape artists, being able to evade some of the antibodies produced after coronavirus vaccinations and infections, including infections caused by some earlier versions of Omicron. That could explain why these subvariants have spread even faster than others in the Omicron family. But there isn’t much evidence yet that they cause more serious illness.
The sub-variants BA.4 and BA.5 have been detected around the world and led to a surge in cases in South Africa in the spring, despite widespread pre-existing immunity to the virus. The wave was not as high as the earlier waves from South Africa, and the number of deaths did not increase as much. Last week, South Africa repealed rules requiring masks in indoor public spaces.
In recent weeks, more than 100,000 new coronavirus cases have been reported on average in the United States each day, according to a DailyExpertNews database, a figure that captures only part of the true number. Many infections are not counted in official reports. Some scientists estimate that the current wave of cases is the second largest from the pandemic.
On Monday, hospital admissions in the United States had jumped 6 percent in the past two weeks, to an average of more than 31,000 a day, according to federal data. The number of new deaths has averaged below 400 a day, data from state and local health agencies shows. That’s a fraction of the thousands observed daily during the wintry Omicron peak.
“But in my mind, 250 deaths a day is still too much,” said Dr. Rochelle Walensky, the CDC director, last week in Aspen, Colo. “The deaths we see are generally among people who are either elderly, frail, many comorbidities, who have had many vaccinations, or people who have not been vaccinated.”
Many Americans with risk factors have said they feel ignored and abandoned as their governments and neighbors have sought a return to normal.
As always, the spread of the virus is a regional matter. Known cases have been declining for weeks in the Northeast and Midwest, while cases are rising in the South and West.
Public health regulations continue to be lifted across the country, including the end on Saturday of an indoor mask mandate for Alameda County, the second most populous county in the San Francisco Bay Area. In New York City, Broadway theaters – all but one – will stop their mask requirements from Friday. Even the long-standing requirement to test for the coronavirus before flying into the United States from abroad was dropped this month.
While the recent availability of vaccines for children ages 6 months to 5 years has been a welcome development for many parents and nurseries, experts do not expect the availability of pediatric doses to change the overall trajectory of the pandemic in the United States.
The natural decline in vaccine protection against infection over time, along with the immune evasion of BA.4 and BA.5, could explain why these subvariants have been able to spread rapidly. It has also given urgency to the development of Omicron-targeted boosters. Although vaccine manufacturers have rushed to develop these, they are based on earlier versions of Omicron, and it was not yet clear how well they could protect against infection with BA.4 and BA.5.
Preliminary evidence from laboratory studies suggests that unvaccinated people infected with the original version of Omicron, known as BA.1, can be easily re-infected by BA.4 or BA.5. Vaccinated people are likely to do slightly better, the study suggests.
But as the virus evolves, no one can say whether revamped vaccines could be obsolete by the time they become available.
“What we don’t know is what’s going to happen in the fall with a new vaccine,” said Dr. Walensky in Aspen. “I think we’re going to need more vaccines.”
