The signoff Friday by CDC Director Rochelle Walensky will lead to a significant widening of the U.S. booster campaign that health officials hope will remove confusion and offer people more protection ahead of holiday gatherings and travel as new daily Covid-19 cases are beginning to rise again.

“Booster shots have demonstrated the ability to safely increase people’s protection against infection and severe outcomes and are an important public health tool to strengthen our defenses against the virus as we enter the winter holidays,” Dr. Walensky said.

Her decision comes after the Food and Drug Administration authorized the extra Pfizer-BioNTech and Moderna doses for all adults earlier in the day, and health experts advising the CDC then voted 11-0 to recommend them.

The advisory panel said the vaccines should be available to all adults and voted unanimously that everyone over 50 years old should get them.

Health authorities have encouraged the extra dose to strengthen people’s immune defenses against the virus.

Supplies should be readily available, according to federal and state health officials. The U.S. has bought a total of 600 million Pfizer-BioNTech doses, and 500 million Moderna doses.

Adults who got the Johnson & Johnson vaccine are already eligible for Pfizer-BioNTech and Moderna boosters.

The FDA regulates whether a vaccine works safely enough to be used outside testing. Many doctors, pharmacies and other vaccination sites follow the direction of the CDC, which guides the practice of medicine and public health.

The latest moves will essentially make an additional dose a standard part of Covid-19 vaccinations now, though some people in the U.S. had found ways to get boosters even if they weren’t eligible and some states widened eligibility.

Federal health authorities have been expanding access to boosters in a rapid—and for many people, confusing—series of moves aimed at shoring up people’s immune defenses to help the U.S. stay ahead of the pandemic.

The Biden administration had aimed to make boosters broadly available in September. Yet its own health agencies have moved more deliberately, clearing boosters for people with weakened immune systems and then high-risk adults as evidence in support of the moves emerged.

One factor driving the push is that making boosters available to all adults will clear up confusion about who should get the doses.

“Streamlining the eligibility criteria and making booster doses available to all individuals 18 years of age and older will also help to eliminate confusion about who may receive a booster dose and ensure booster doses are available to all who may need one,” said Peter Marks, director of the FDA center that oversees vaccines.

The latest authorizations apply to adults at least six months past their second shot, whether they got the Pfizer-BioNTech or Moderna vaccine initially.

The booster expansion comes after the Delta-driven increases over the summer have receded in most states. Some places have recently experienced an uptick in cases, raising the average number of daily cases nationally. That has led to concerns about a winter surge.

Behind the push for boosters is some research finding that the protection that vaccination provides against symptomatic infections wanes after six months or so.

Eric Topol, director of the Scripps Research Translational Institute in La Jolla, Calif., pointed to data from Israel and other recent studies indicating that boosters reduced the risk of hospitalization and death in people at least 40 years old and symptomatic infections among younger people.

“This booster has a big bang for blocking infections, and that’s the whole point, that’s how you break the transmission chain,” he said.

Yet other health experts say that increasing primary vaccinations, not boosters, is the best way to protect everyone and reduce the spread of the virus, since studies show community transmission is mostly driven by unvaccinated people.

Vaccines weren’t designed to prevent infections, the critics say, but rather prevent severe disease and hospitalizations.

“I think the goal should be to reduce severe disease, hospitalization and death. We have not even achieved that right now and that’s what we need to focus on,” said Celine Gounder, an infectious-disease specialist at Bellevue Hospital Center in New York.

She said available data supports boosting people over 65 years and immunocompromised people but not the broader population.

Despite the debate, many people have sought booster shots, including those who might not fit the criteria outlined by health authorities.

A handful of states and cities, including Arkansas, West Virginia and New York City, have also expanded booster eligibility beyond federal government guidelines in an effort to prevent winter surges.

Since the FDA began authorizing boosters, more than 32 million people have received the extra doses, including more than 19 million people who received Pfizer-BioNTech’s and more than 13 million who got Moderna’s, according to the CDC.

The booster expansion simplifies the currently confusing recommendations, said Gregory Poland, director of the Mayo Clinic’s vaccine research group. “It makes for very easy, clear public-health messaging: If you’re 18 or over, get a booster,” he said.

The CDC’s advisory panel, called the Advisory Committee on Immunization Practices, is a group of medical and public-health experts who make recommendations to the agency about how vaccines should be used in the U.S.

In presentations to the panel, officials from Pfizer and Moderna said side effects after the booster doses are similar to those reported after previous doses.

People reported fewer side effects after getting a third dose of either the Pfizer-BioNTech or Moderna vaccines as compared with after the second dose, said Tom Shimabukuro, a CDC vaccine expert who presented data from a federal safety database.

The data also indicated that people who were boosted with Moderna, regardless of their first vaccines, reported more side effects than those boosted with Pfizer.

The risk of myocarditis after getting a Pfizer-BioNTech booster dose appears lower than after a second dose of the vaccine, according to Keipp Talbot, a CDC panel member and associate professor of medicine at Vanderbilt University. She said there is limited data available to assess the risk of myocarditis after a Moderna booster dose.

Some U.S. safety databases show a heightened risk of myocarditis in younger men who received the Moderna vaccine as compared with the Pfizer-BioNTech vaccine. The FDA has delayed clearing the shot for adolescents while it investigates whether there is a heightened risk of myocarditis. The Moderna booster dose is half the dose of the first two shots.

Sara Oliver, another CDC official presenting to the panel, said there is limited data from Israel to suggest that the booster doses may help decrease community transmission. Though the effect may not be permanent, she said even a temporary decrease would be beneficial over the holiday and winter season.

In September, the FDA cleared a third dose of the Pfizer-BioNTech vaccine for adults who are 65 years and older or are at high risk of severe disease and death, including because of their jobs or where they live.

The government has also endorsed additional shots from Moderna for high-risk people, and is backing mixing and matching extra doses of the three vaccines cleared for use.

In August, Pfizer and BioNTech sought clearance of boosters for people 16 years and older, but the agency limited the extra doses to the elderly and adults who were at high risk after outside scientific advisers said they weren’t convinced that broad boosters were necessary at the time.

Since then, though, Pfizer and BioNTech shared results from a study of about 10,000 subjects 16 years and older that found the booster shot was 95.6% effective at preventing symptomatic Covid-19.

Researchers also found the additional dose was safe and tolerable, and consistent with what was known about the vaccine, the companies said.

Last month, the FDA cleared a booster shot of Moderna at half the dose of each of the first two shots. Moderna sought authorization for seniors and high-risk adults after Pfizer-BioNTech’s booster was approved for those people.

In Moderna’s booster application, the company presented data, from a study of nearly 300 people, indicating a half-dose booster given at least six months after initial vaccination restored antibody levels.

This story has been published from a wire agency feed without modifications to the text