Current booster shots of the coronavirus vaccine are based on the original version of the virus. (Allison Shelley for The Washington Post)
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Second booster shots of the coronavirus vaccine for people younger than 50 are on hold as the Biden administration tries to accelerate a fall vaccination campaign using reformulated shots that target the now-dominant omicron subvariants, according to federal health officials.

Officials are hoping vaccine makers — Moderna and Pfizer and its German partner, BioNTech — are able to make the updated shots available as soon as early to mid-September instead of later in the fall, said three officials who spoke on the condition of anonymity because they were not authorized to talk about the issue.

The retooled boosters will contain components from the omicron subvariants BA.4 and BA.5 as well as the original formula, which was based on the version of the virus that spread globally in early 2020. The hope is that the redesigned boosters will be more effective in dealing with an evolving virus.

In late June, FDA advisers recommended including an omicron component in retooled boosters, and the agency directed the manufacturers to do so. The companies indicated they would probably deliver the new shots in October. But since then, officials have urged the firms to move faster in producing the shots. If the new boosters are available by early to mid-September, the officials said, it is unlikely the administration would authorize a second dose of the current boosters for people younger than 50.

A final decision has not been made; officials are waiting for information from the manufacturers on whether there would be an adequate supply of reformulated shots if the fall campaign began earlier than expected. A decision is expected within days.

The FDA said it is evaluating the current situation, including data showing an increase in hospitalizations, and will make decisions on boosters based on all of the available evidence.

Moderna spokesman Chris Ridley said the company is committed to accelerating the supply of its reformulated vaccines “to meet the needs of regulators and public health demands around the world.” Pfizer declined to comment on administration vaccine decisions.

Currently, the only groups eligible for a second coronavirus booster are people 50 and older and those 12 and older with impaired immune systems.

Earlier this month, administration officials said they were weighing a plan to allow all adults to receive a second booster to blunt a virus surge fueled by ever-more-contagious omicron subvariants such as BA. 5 that evade some immune protections and have increased the risk of reinfections.

Ashish Jha, the White House coronavirus coordinator, and Anthony S. Fauci, the White House chief medical adviser, favored making booster shots more widely available this summer and calling for a quick decision. But Peter Marks, the top FDA vaccine official, had some concerns, officials said.

As the debate dragged into late July, officials have grown increasingly worried that the window is closing to encourage younger adults to receive a second booster shot now and then a reformulated shot later this year.

Rochelle Walensky, director of the Centers for Disease Control and Prevention, said Friday on Washington Post Live that her agency is talking to the FDA about a second booster for all adults but that it is ultimately the FDA’s decision.

“There would have to be action from the FDA to authorize a fourth dose for people under 50,” Walensky said. “In the meantime, another thing that we are doing is planning for the fall and understanding what the implications are, and where we are going for the fall, which is just about six weeks away.”

Some outside experts endorsed the idea of allowing all adults to get a second dose of the current booster — especially because the protection provided by the first boosters is waning. That would also allow the Biden administration to use vaccine doses that are reaching their expiration dates and would otherwise be discarded.

But other experts warned that a second dose of the current booster would not provide a big benefit and might do some harm. Paul A. Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia and an outside adviser to the FDA, said recently that repeatedly administering the same vaccine could lead to a phenomenon known as “imprinting,” in which an individual’s immune system develops a highly targeted response to earlier versions of a virus and fails to adapt as that virus evolves.

The federal government has agreed to purchase 105 million doses of Pfizer-BioNTech’s rebooted vaccine for $3.2 billion. At $30.50 a dose, that is a premium over the initial contracts the government made for the original vaccine in 2020, when the vaccines were $19.50 per dose.

The government is expected to sign a contract with Moderna shortly.

Coronavirus: What you need to know

End of the public health emergency: The Biden administration ended the public health emergency for the coronavirus pandemic on May 11, just days after WHO said it would no longer classify the coronavirus pandemic as a public health emergency. Here’s what the end of the covid public health emergency means for you.

Tracking covid cases, deaths: Covid-19 was the fourth leading cause of death in the United States last year with covid deaths dropping 47 percent between 2021 and 2022. See the latest covid numbers in the U.S. and across the world.

The latest on coronavirus boosters: The FDA cleared the way for people who are at least 65 or immune-compromised to receive a second updated booster shot for the coronavirus. Here’s who should get the second covid booster and when.

New covid variant: A new coronavirus subvariant, XBB. 1.16, has been designated as a “variant under monitoring” by the World Health Organization. The latest omicron offshoot is particularly prevalent in India. Here’s what you need to know about Arcturus.

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