• The Center for Disease Control and Prevention cleared the reformulated omicron boosters Thursday.
• An independent committee recommended shots, which target the dominant omicron BA.5 subvariant.
• Pfizer's omicron boosters are for people ages 12 and older, while Moderna's updated shots are for adults ages 18 and older.
• Vaccinations are expected to start next week.

The Centers for Disease Control and Prevention cleared reformulated Covid shots that target the latest omicron subvariants for the fall, making it possible for many people to get an extra booster within days.

The agency's independent committee on vaccines voted 13 to 1 earlier Thursday in favor of the shots after reviewing the available safety and effectiveness data over an almost seven-hour-long meeting. CDC Director Dr. Rochelle Walensky signed off on the shots a few hours later, clearing the way for pharmacies to soon start administering the shots.

Pfizer's omicron boosters were OKed for people ages 12 and older, while Moderna's updated shots were authorized for people ages 18 and older. The eligible age groups can receive the boosters at least two months after completing their primary series or their most recent booster with the old shots.

Walensky said her decision 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," she said in a statement.

Pfizer plans to ask the Food and Drug Administration to also authorize the new boosters for children ages 5 to 11 years old in early October, company executives told the committee Thursday.

The original vaccines will no longer be used as a booster in people ages 12 and older now that the reformulated shots are coming online.

Public health officials are expecting another wave of Covd infection this fall as immunity from the old vaccines wanes off, more contagious omicron subvariants spread, and people spend more time indoors as the weather turns colder and families gather for the holidays.

The CDC and the FDA hope the new boosters will provide more durable protection against infection, mild illness and severe disease. The reformulated shots target omicron BA.5, the dominant variant of Covid as well as the strain that emerged in China more than two years ago.

The U.S so far has secured 171 million doses of Pfizer's and Moderna's new boosters. More than 200 million people are eligible for the shots, according to the CDC. Dr. Sara Oliver, a CDC official, told the committee Thursday that there should be enough supply of the vaccine to meet demand this fall.

No omicron BA.5 human data

There is no data from human trials on the new BA.5 boosters, so it's unclear how they will perform in the real world. The CDC and FDA used human data from clinical trials for shots targeting the original version of omicron, BA.1, which triggered a stronger immune response than the old vaccines.

Pfizer and Moderna were originally developing omicron boosters to target BA.1, but the FDA asked the companies to switch gears in June and develop BA.5 shots instead after the subvariant became dominant. The decision to focus on BA.5 did not leave enough time to wait for data from human trials ahead of a fall vaccine rollout.

The lack of human data for the BA.5 shots has caused some controversy, but Dr. Peter Marks, a senior FDA official, said the agency followed the same process used for years with strain changes for flu vaccines. Marks said on Wednesday that flu vaccine strains are also changed without human clinical data.

Dr. Pablo Sanchez, the only committee member who voted against the shots, called the recommendation premature and said the U.S. should have waited for human data before proceeding with the boosters.

"There's a lot of vaccine hesitancy already — we need the human data," said Sanchez, a professor of pediatrics at Ohio State University. But Sanchez said he believes the new boosters are safe and he will likely receive one himself.

Panel member Dr. Oliver Brooks, chief medical officer at Watts HealthCare Corporation in Los Angeles, questioned why the FDA decided to go with a BA.5 vaccine when clinical data is available for the BA.1 shots that the vaccine makers were originally developing. Brooks ended up voting in favor the shots.

But Dr. Sarah Long, also a committee member, said there's no reason to expect the BA.5 boosters will be inferior to the old shots since they also include the original Covid strain, and they have potential to reduce hospitalizations and deaths heading into the fall and winter. Long also voted in favor.

Mouse studies

Officials at the FDA and CDC have said the omicron BA.1 and omicron BA.5 boosters are similar enough that the immune response data from the BA.1 shot should give a good indication of how the BA.5 shots will perform. Omicron BA.1 and BA.5 are closely related with a four-mutation difference, according to Dr. Jacqueline Miller, who works on vaccine development at Moderna.

Moderna completed enrollment in clinical trials on the BA.5 shots last week and should have results by the end of the year, Miller told the CDC committee on Thursday. Pfizer's clinical trial is also ongoing, though company hasn't said when it expects results.

The health agencies also reviewed data on the BA.5 shots from mouse studies. Moderna presented data showing that the BA.5 shots increased antibodies in mice more than fourfold compared with the old shots. The mice express the same cell protein as humans that the virus latches onto. Pfizer's BA.5 booster increased antibodies 2.6 fold in mice compared with the original vaccine.

Safety

The most common side effects from the human trials of the BA.1 shots was pain, redness, swelling at the injection site, fatigue, headaches, muscle pain, joint pain, chills, nausea, vomiting and fever, according to the FDA.

Oliver, the CDC official, told the committee that health officials do not expect any difference in the safety profile of the BA.1 and BA.5 shots given that subvariants differ only by a few mutations.

But Oliver noted that the risk of myocarditis following a BA.5 booster shot is unknown. There is an elevated risk of myocarditis among young men and adolescent boys following the second dose of Pfizer's and Moderna's shots but the risk of myocarditis from Covid infection is higher, according to the CDC.

"We know that the myocarditis risk is unknown but anticipate a similar risk to that seen after the monovalent vaccines," Oliver said. The monovalent vaccines are the old shots that have been administered to millions of people in the U.S. over the past two years.

Old vaccines losing effectiveness

The original vaccines, which were first authorized in December 2020, are no longer providing meaningful protection against infection because the virus has mutated so much over the past two years. The shots were developed against the first strain that emerged in China, so they are no longer matched to target the omicron subvariants that are spreading.

Infections, hospitalizations and deaths have declined dramatically since the massive wave of omicron infection last winter, but have plateaued this summer at a stubbornly high level. Omicron BA.5 is the most contagious and immune evasive variant yet, and breakthrough infections have become increasingly common as a consequence.

The old vaccines effectiveness against hospitalization also declined after omicron BA.5 became dominant. A third dose was 77% effective at prevention hospitalization four months after receiving the shot, but protection declined after 120 day to as low as 34%, according to CDC data. A fourth dose in people ages 50 and older was 56% effective at preventing hospitalization after four months.

Deaths and hospitalizations from Covid among people ages 65 and older have increased since April, according to Heather Scobie, a CDC epidemiologist who presented data during Thursday's meeting. Deaths have risen in particular among people ages 75 and older, Scobie said.

The CDC has shifted to a more targeted public health response with an emphasis on protecting the most vulnerable — the elderly, people with serious medical conditions and those who have weak immune systems. Although there's no data on the real-world effectiveness of the new boosters, the U.S. is moving rapidly to roll them out in the hope that they will protect people this fall.