What does the BA.5 subvariant mean for America?

A highly contagious variant of the coronavirus threatens new infections in the United States, even among people who have recently recovered from the virus.

Known as a subtype of Omicron BA.5 now dominatesAlong with another subtype, BA.4, it drives cases and hospitalizations, according to federal estimates released Tuesday.

Although the popularity of home testing means that the actual infection rate is significantly underreported, the share of tests that come back positive is shooting upwards and is now higher than in other waves of the epidemic. According to the CDC, the risk of Covid-19 is increasing across much of the country.

“I think there’s an underestimation of what it’s going to do to the country, and it’s already having an effect,” said Eric Topol, professor of molecular medicine at Scripps Research. Written about the subgenre.

BA.5 and BA.4, subtypes of the Omicron variant that took the world by storm this winter, are versions of the virus that are more efficient at evading immunity from previous infections and vaccines. Both types have mutations in their spike proteins that are sufficiently different from earlier versions of the virus that some antibodies can block them.

Waves of infection – and the immunity that accompanies them – vary across countries and make for imperfect comparisons. Vaccination rates also vary. But where BA.4 and BA.5 predominate for weeks or months, secondary variants have caused an increase in cases and hospitalizations, despite some population immunity from previous waves.

The CDC says there is no evidence yet that BA.4 or BA.5 is inherently more severe than other omicron subtypes, but as more people become infected, the number of hospitalizations due to the virus may rise.

Previous infection with another form of the omicron variant confers some degree of immunity, Dr. Tobol said, and may explain why cases in the United States have not yet begun to take off in earnest. “But nothing like what we expected,” he said. Omicron subvariants represent escape from previous waves of virus, making previous infection more likely to protect against reinfection.

In Portugal, where vaccination rates are higher than in the US, cases rose sharply after BA.5 dominated in May, and hospitalizations neared the previous Omicron peak.

Before BA.4 and BA.5 dominated South Africa in April, research suggested 98 percent of the population Some antibodies were present from vaccination or previous infection or both.

Even with those protective antibodies, many people in the country are still infected with BA.4 and BA.5, and sub-variants cause small increases in cases, hospitalizations and deaths.

Places emerging from significant spring waves of the virus may also not be spared. A different Omicron sub-variant, BA.2, has erupted in large numbers in several countries in Europe, leading to new hospitalizations and deaths that recently peaked in April. Yet in those countries, cases are rising again as BA.5 predominates.

Experts say it’s too early to fully predict what the latest subtypes might bring to the U.S., which had more recent waves of the virus in May and June, driven by another subvariant called BA.2 and BA.2.12.1. The high shares of recent infections from BA.2.12.1 are unusual in the United States, which is now experiencing waves of BA.4 and BA.5 infections.

The U.S. has a lower vaccination rate than many of those countries, and a much lower share of seniors who have received one or two booster shots.

“A wave is hitting, there’s no question about it,” Dr. Topol said. “My concern is its length.”

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