Omicron submarine BA.4 and BA.5 together have become influential in the United States,

Continuing their rapid advance across the United States, Omicron submarines known as BA.4 and BA.5 together have become influential in new coronavirus cases, according to new estimates from the Centers for Disease Control and Prevention on Tuesday.

As of the week ending Saturday, BA.4 was 15.7 percent new cases, and BA.5 was 36.6 percent, which accounted for about 52 percent of new cases in the United States, experts said, adding that the number will increase in the coming weeks.

The figures released on Tuesday morning are based on modeling and could be corrected as more data arrives, which happened in late December, when the agency missed the forecast mark.

The day the independent advisers to the Food and Drug Administration met Tuesday to consider updating the vaccine, including a booster shot for Americans, could better match some versions of Omicron, although the virus could evolve again in the fall. .

Less than six months after the first detection of BA.4 and BA.5 in South Africa, the two submarines surpassed the previous two Omicron submarines in the United States, including BA.2, which was the conventional version for a time. Before this spring. The other, BA.2.12.1, was dominant alone in the week ending June 18, according to CDC estimates. Since Omicron came to the United States, it has increased the number of cases in the winter. Earlier, the Delta variant had been dominant in the United States since the beginning of summer.

BA.4 and BA.5 demonstrate the qualities of escape artists, who are able to avoid coronavirus vaccines and some antibodies produced after infection, including infections caused by some earlier versions of Omicron. This may explain why these submarines spread faster than others in the Omicron family. But not much evidence has yet been found that they cause more deadly diseases.

BA.4 and BA.5 subverbets have been identified around the world, and they cause an increase in cases in South Africa in the spring, despite widespread pre-existing immunity to the virus. The waves were not as high as in South Africa’s previous waves and the death toll did not rise as much. Last week, South Africa repealed its rules that required masks in indoor public spaces.

That pattern appears to be holding, so far, in the United States.

In recent weeks, an average of more than 100,000 new coronavirus cases have been reported each day in the United States, a statistic that captures only a fraction of the actual number, according to a New York Times database. There are countless infections in official reports. Some scientists have speculated that the current wave of cases is the second largest of the epidemics.

As of Monday, hospital admissions in the United States have risen 6 percent to an average of more than 31,000 per day over the past two weeks, according to federal data. Data from state and local health agencies show that new deaths are below 400 per day on average. This is a fraction of the thousands seen every day at the Winter Omicron peak.

“But I think 250 deaths a day is still a lot more,” Dr. Rochelle Walenski, CDC director, said last week in Aspen, Colo. Weak, a lot of comorbidities, who have been vaccinated a lot or who have not been vaccinated. “

Many Americans, including at risk, say their governments and neighbors feel neglected and abandoned in order to return to normalcy.

As always, the spread of the virus is a regional matter. In the Northeast and Midwest, known cases have been declining for weeks, while in the South and West, cases are on the rise.

Across the country, public health regulations continue to be repealed, including the end of an indoor mask mandate for Alameda County, the second most populous county in the San Francisco Bay Area, on Saturday. In New York City, Broadway theaters – save for one – are retiring their mask requirements from Friday. The long-standing need to test for coronavirus even before flying to the United States from abroad was eliminated this month.

Although in recent times the availability of vaccines for children aged 6 months to 5 years has been a welcome development for many parents and day care centers, experts do not expect that the availability of baby doses will change the overall course of the epidemic in the United States.

The natural decline in vaccine protection against infection over time, along with the immunity of BA.4 and BA.5, may explain why these subverbs have been able to spread so rapidly. This has given impetus 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 is not yet clear how well they can protect against BA.4 and BA.5 infections.

Preliminary evidence from laboratory research suggests that immunized people who were infected with the original version of Amicron, known as BA.1, could easily be re-infected with BA.4 or BA.5. Vaccinated people are more likely to get better, research suggests.

But as the virus develops, no one can say whether the reconstituted vaccines will become obsolete when they become available.

“What we don’t know is what’s going to happen with a new vaccine in the fall,” said Dr. Walensky while in Aspen. “I think we need more vaccines.”

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