The Food and Drug Administration on Wednesday authorized Pfizer’s and Moderna’s updated COVID-19 booster shots that target the BA.4 and BA.5 omicron variants.

On Thursday, an advisory panel for the Centers for Disease Control and Prevention also recommended the vaccines. The CDC signed off on the panel's recommendation shortly after, meaning shots could be available as soon as Friday.

The CDC’s Advisory Committee on Immunization Practices, which votes on whether the agency should issue recommendations, held meetings Thursday to discuss approving the vaccines. CDC Director Dr. Rochelle Walensky quickly signed off on the panel's recommendation, clearing the way for shots to begin.

"The updated COVID-19 boosters are formulated to better protect against the most recently circulating COVID-19 variant," Walensky said in a statement. "They can help restore protection that has waned since previous vaccination and were designed to provide broader protection against newer variants. This recommendation followed a comprehensive scientific evaluation and robust scientific discussion. If you are eligible, there is no bad time to get your COVID-19 booster and I strongly encourage you to receive it."

The Pfizer and Moderna boosters will be the first reformulated coronavirus vaccines to hit the market during the pandemic.

Dr. Anthony Fauci, the nation's top infectious disease expert and President Joe Biden's chief medical adviser, said in an interview Friday that it was "important" for Americans to get these updated shots, particularly because the protection of the vaccine wanes over time.

"I feel strongly that [getting boosted is] something that we need to do to maintain the protection of the individual and the American public," Dr. Fauci said on MSNBC on Friday. "And we ultimately would like to do, and I think it would be an important strategy, since for most of the people – not everyone because there are immunocompromised who might need it more often – that we want to get into the cadence and the rhythm of about once per year, get an annual shot, similar somewhat to what we do with the flu shot."

The advisers ultimately voted 13-1 to recommend the updated vaccines, with some originally expressing concern that there was not sufficient data to warrant approval. 

"We've been extrapolating the data that has been seen with the bivalent BA.1, and hopefully, we'll have similar data for BA.4 and BA.5.," Dr. Pablo Sánchez, a professor of pediatrics at Ohio State University who serves on the advisory committee, said in part. “So I'm just concerned about that extrapolation [...] and ultimately, I really don't want to establish a precedent of recommending a vaccine that we don't have clinical data.”

Sánchez was ultimately the only opposing vote, saying he felt the decision “was a bit premature,” though he acknowledged the vaccines were likely to be found safe through rigorous human testing. But other panel members agreed that waiting to approve the updated vaccine until clinical data is available, which will not be until November, would prove more harmful in the long run. 

"I just would like to remind the committee that every year, we use influenza vaccines that are based on new strains without clinical studies being done," Dr. Melinda Wharton, who works for the National Center for Immunization and Respiratory Diseases and serves as executive secretary of the ACIP panel, said in part.

Both of the shots are bivalent, targeting the original 2019 strain as well as BA.4 and BA.5, which today account for 99.8% of COVID-19 infections in the United States. The FDA amended its emergency use authorizations for the vaccines to include the reformulated boosters and also withdrew its authorization for the previous booster shots for people ages 12 and older.

“The COVID-19 vaccines, including boosters, continue to save countless lives and prevent the most serious outcomes (hospitalization and death) of COVID-19,” FDA Commissioner Robert M. Califf said in a statement. “As we head into fall and begin to spend more time indoors, we strongly encourage anyone who is eligible to consider receiving a booster dose with a bivalent COVID-19 vaccine to provide better protection against currently circulating variants.”

Pfizer’s booster, which is manufactured in partnership with the German company BioNTech, would be available to people 12 and older, while individuals 18 and older would be eligible for Moderna’s. The FDA said it will work quickly to evaluate future data and submissions for bivalent boosters for other age groups.

Vaccine effectiveness wanes over time. The CDC recommends two boosters for most Americans age 50 and older, and one booster for most people 5 to 49.

Earlier this year, Pfizer and Moderna approached the FDA with bivalent boosters that targeted the original version of the virus as well as the first strain of the omicron variant, BA.1. However, the FDA in June directed the vaccine makers to change their designs to start targeting BA.4 and BA.5. 

The FDA said it based its decision Wednesday on data from the original vaccines, clinical data for the BA.1 version of the vaccine and nonclinical data from the BA.4/BA.5  shots.

“The FDA considers such data as relevant and supportive of vaccines containing a component of the omicron variant BA.4 and BA.5 lineages,” the agency’s announcement said. 

The agency said it analyzed data from Moderna and Pfizer that compared the immune responses of people who received the BA.1 bivalent booster to others who were given the original, monovalent shot. In both studies, the immune response against BA.1 was stronger in those who received the updated shot, the FDA said.

Moderna evaluated around 600 volunteers 18 and older, while Pfizer studied about 600 people 55 and older. Both companies focused on individuals who had received a two-dose primary series and one earlier booster.

“The FDA has been planning for the possibility that the composition of the COVID-19 vaccines would need to be modified to address circulating variants,” said Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research. “We sought input from our outside experts on the inclusion of an omicron component in COVID-19 boosters to provide better protection against COVID-19. We have worked closely with the vaccine manufacturers to ensure the development of these updated boosters was done safely and efficiently. The FDA has extensive experience with strain changes for annual influenza vaccines. We are confident in the evidence supporting these authorizations.

“The public can be assured that a great deal of care has been taken by the FDA to ensure that these bivalent COVID-19 vaccines meet our rigorous safety, effectiveness and manufacturing quality standards for emergency use authorization,” Marks added.

The side effects to the reformulated boosters are similar to those seen in the original vaccines. The most common are pain, redness and swelling at the injection site, fatigue, headache, muscle pain, joint pain, chills, swelling of the lymph nodes, nausea and fever.

Both the Moderna and Pfizer shots use mRNA technology, which involve a specific piece of genetic material that instructs cells in the body to make a distinctive “spike” protein of the virus. The spike proteins for BA.4 and BA.5 are identical.

The U.S. is reporting more than 82,000 COVID-19 infections a day, but that is believed to be a vast undercount due to unreported at-home tests and fewer health agencies and states providing updates. The seven-day average for COVID-19 deaths is 387.

Currently, around 67% of the total U.S. population is fully vaccinated against COVID-19, but only 48% have received their first booster dose, according to CDC data. And with many Americans tired of hearing about the pandemic, the White House is facing questions about how the administration will convince people to get the variant-specific booster should it be authorized this fall. 

White House Press Secretary Karine Jean-Pierre on Wednesday said the administration will lean heavily on the lessons learned from its vaccination outreach campaign at the outset of Biden's time in office, focusing the new push primarily on educating doctors and other individuals who are "trusted voices" in their communities to help encourage the booster doses. 

"We're planning a public education campaign building on lessons we've learned, as I just stated, and focusing on those most at risk," she told reporters at an afternoon press briefing. "This will include leveraging deep partnerships, as I mentioned, across sectors to meet people where they are."

As far as new booster availability, Jean-Pierre said the administration has been "working for months" to prepare for the vaccine approval, adding that states were allowed to preemptively order some vaccines ahead of the CDC's possible green light later this week -- and every state has done so. 

"To make sure vaccines get to communities quickly, primary care providers and community health centers and rural health clinics across the country are able to order vaccines directly from the federal government," she added.