The White House on Tuesday urged Americans over age 50 to get vaccination boosters against Covid-19 as the fast-spreading Omicron BA.5 subvariant takes hold across the United States and said doing so now would not preclude another shot this fall.
US health officials warned that the variant, which makes up a majority of cases in the country, was more resistant than previous variants to immunity, including from prior Covid-19 infection.
BA.5 is estimated to account for 65% of the coronavirus variants circulating in the United States as of last week, said Rochelle Walensky, the director of the US Centers for Disease Control and Prevention (CDC).
Officials urged people who are 50 years old or older to get a booster shot and said that would not prevent them from getting another "bivalent" booster designed to fend off Omicron more specifically later this year.
"If you've not gotten a shot in 2022, first of all, getting one now protects you for the rest of the summer, into the fall. Second, it does not preclude you from being able to get a bivalent vaccine in the fall," Dr Ashish Jha, the White House's Covid-19 response coordinator, told reporters at a briefing.
The BA.5 and BA.4 subvariants together accounted for more than 80% of circulating variants last week, with BA.4 making up 16%, Walensky said at the same briefing.
The seven-day average of daily Covid-19 hospital admissions has doubled in the United States since early May, she said.
BA.5 does not appear to be associated with greater disease severity or hospitalizations compared to the most recent subvariants, said Dr Anthony Fauci, an infectious disease expert who is the chief medical adviser to President Joe Biden.
"Variants will continue to emerge if the virus circulates globally and in this country. We should not let it disrupt our lives, but we cannot deny that it is a reality that we need to deal with," Fauci said.
The White House said BA.5's wide circulation means new cases would likely rise in the coming weeks.
"Immunity wanes, whether that's immunity following infection or immunity following vaccine, even though the immediate protection following infection or vaccine is generally good protection," Fauci said. "If you were infected with BA.1, you really don't have a lot of good protection against BA.4/5."
The United States approved boosters in March, citing data from Israeli studies that showed that a fourth shot prevented hospitalization and death in older people. Scientists have questioned whether it is needed by younger, healthy people and Israeli data did not show an advantage in this group.
The US Food and Drug Administration (FDA) has recommended Covid-19 vaccine manufacturers change the design of their booster shots to better combat the BA.4 and BA.5 subvariants.
Health regulators and White House officials are discussing making people under the age of 50 eligible to get the booster shot, but the final decision rests with the FDA and the CDC, Fauci said.