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The Biden administration on Tuesday urged the public to strengthen their protections against Covid-19, noting that the BA.5 subvariant of Omicron has become the dominant strain in the country.

At a briefing Tuesday, health officials outlined their plan to combat the latest form of the coronavirus to pose a threat, emphasizing existing tools like vaccines and boosters, testing, and treatments.

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“BA.5 is something we’re closely monitoring, and most importantly, we know how to manage it,” said Ashish Jha, the White House’s Covid-19 response coordinator.

The latest estimates indicate BA.5 is now responsible for about 65% of U.S. Covid-19 cases, while its closely related cousin, BA.4, is accounting for about 16% of infections, said Rochelle Walensky, the director of the Centers for Disease Control and Prevention.

BA.5 has become dominant in the United States, as well as in much of the world, because it is so adept at establishing infections in people who’ve previously had Covid-19 or been vaccinated — even more so than other versions of the virus that also fall under the Omicron umbrella. At the same time, waning immunity from previous infections or past shots leaves people more susceptible to infections, even as vaccine-elicited protection against more severe outcomes is broadly maintained.

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Health officials sought to convey they were on top of BA.5, while underscoring the risks it posed. The strategy outlined Tuesday included improving the accessibility of tools that to varying levels have been available for months, including vaccines and boosters, the antiviral Paxlovid and antibody bebtelovimab, and easy and widespread testing. The White House also mentioned steps it’s taking to protect immunocompromised people — including expanding the availability of the pre-exposure treatment Evusheld — and to encourage building owners to improve ventilation.

“We can prevent serious illness, we can keep people out of the hospital and especially out of the ICU, we can save lives, and we can minimize the disruptions caused by Covid-19,” Jha said, highlighting the effectiveness of vaccines and treatments. “And even in the face of BA.5, the tools we have continue to work.”

Jha also said people should take a test before attending large indoor gatherings or visiting an at-risk person.

BA.5 is raising concerns not only for how adept it is at infecting people, but also because it became dominant at a time when the virus was already transmitting at high levels. For several weeks, average daily infection counts have hovered around 100,000, though experts say that’s a massive undercount. Some researchers say infections could be some 10 times that, as at-home tests, rolled-back testing programs, and people forgoing tests limit the reliability of that figure.

Health officials have urged Americans to pay attention to the CDC’s tracking of Covid-19 levels in their community, with people living in areas of high transmission — roughly one-third of the population now — being urged to wear masks in public indoor settings. But outside experts have argued that given how much transmission is going undetected, the map underestimates the true risk of infection in a given location.

Walensky said there were about 5,100 Covid-19 related hospitalizations per day — a slight increase since last week, but a doubling since early May.

Daily deaths, meanwhile, have bounced between 300 and 350 for several weeks. It’s a reflection of how, with the vast majority of people having some level of protection because of vaccination or past infection or both, the individual risk of each Covid-19 infection has been cut. But still, because of the sheer number of cases, the virus is still killing a few thousand people each week, mostly older people or those with other health conditions.

Of the deaths, Jha said, “That is unacceptable. It’s too high.”

The takeover by BA.5 represents the latest in a series of handoffs between which Omicron lineage is driving cases in the United States, dating back to BA.1 last year, to BA.2, BA.2.12.1, and now BA.5 and BA.4.

The Food and Drug Administration last month recommended that vaccine makers add a component of the spike protein from BA.5 and BA.4 (the two sublineages have essentially identical spike proteins) to their original vaccine formulations, creating a “bivalent” shot that could be used for a fall booster campaign.

Many of the current cases are reinfections or breakthrough infections, given that there are few people who have not yet been infected or vaccinated. Experts have found that protection against infection wanes after a matter of months, and infection with certain variants does not provide much cross-protection against others. People who were infected with BA.1, for example, don’t have much lasting protection against some of the other Omicron subvariants.

While the current vaccines continue to provide strong protection against severe outcomes in most people, as more time passes since people received their last dose and as the virus keeps evolving, certain groups — particularly older people and those with preexisting conditions — become more vulnerable to serious disease even if they have some prior doses or past infections. The trend underscores the importance of booster shots.

But only about a third of people 5 and older have received a primary booster dose so far. The country’s low booster rate was why it had a much more devastating initial Omicron wave in terms of hospitalizations and deaths than many European countries.

“Currently, many Americans are undervaccinated,” Walensky said.

People 50 and older are also eligible for a second booster. Jha stressed that if people in this age group haven’t received a dose in 2022, they should get one now. Doing so would not preclude them from getting variant-specific or bivalent boosters if those shots are made available later this year, he said.

Asked about reports that the administration is considering authorizing second boosters for people under 50, Jha only said any such decision would be made by the FDA and the CDC.

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