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  • Eligible people may soon be able to choose any authorized COVID-19 vaccine for their booster, pending CDC approval.
  • Evidence from the European Union, United Kingdom, and Canada also supports mixed dosing during the initial series.
  • The CDC panel also recommended booster doses for certain Moderna vaccine recipients, and for all Johnson & Johnson recipients 18 years and older.

An expert advisory group for the Centers for Disease Control and Prevention (CDC) voted unanimously today to recommend boosters for certain people who were vaccinated with the Moderna and Johnson & Johnson (J&J) vaccines.

The panel also approved the option for people to get a different vaccine from the one they received during their initial series, also known as heterologous or “mix and match” boosting.

This would allow eligible people who received an mRNA vaccine to get a booster dose of any authorized vaccine 6 months or later after completing their primary series.

Eligible people who received the one-dose J&J vaccine would be able to get a booster dose of that vaccine or an mRNA vaccine at least 2 months after their initial dose.

The panel’s recommendation now goes to CDC director Dr. Rochelle Walensky for a final decision.

The CDC will issue “clinical guidance” for healthcare professionals on how to help people make a decision about which vaccine to get as a booster. This will take into account rare risks associated with specific vaccines, which are higher for certain populations.

The CDC panel’s vote comes a day after the Food and Drug Administration (FDA) authorized boosters of these vaccines, along with mix-and-match boosters.

The FDA had previously authorized booster doses of the Pfizer/BioNTech vaccine for certain groups, which was also approved by the CDC.

The option for mix-and-match boosters will provide greater flexibility at vaccination sites and enable people concerned about the health risks of a certain vaccine to seek out a different brand for their booster.

Last week, an FDA vaccine advisory committee reviewed positive data from a National Institutes of Health (NIH) study on mix-and-match boosters.

Researchers found that people who received any booster saw an increase in immune protection. In addition, people who received a booster different from the vaccine used during their initial series saw a similar — if not better — boost.

Switching to a different vaccine for the booster produced side effects on par with using the same brand.

For the study, researchers recruited 458 adults who had initially been vaccinated with two doses of the Moderna vaccine, two doses of the Pfizer/BioNTech vaccine, or a single dose of the J&J vaccine.

They gave each person one of the three vaccines as a booster. In all, researchers compared nine initial-booster combinations, with about 50 people in each group.

The study was posted online Oct. 15 as a preprint, so it has not yet been peer reviewed.

The results were particularly striking for people who had received a single dose of the J&J vaccine.

J&J recipients who were boosted with a second dose of the vaccine saw a fourfold increase in the level of neutralizing antibodies 15 days after the booster.

In contrast, using Pfizer/BioNTech as the booster raised antibody levels 35-fold, while a Moderna booster increased them by a factor of 76.

People who received a single dose of the J&J vaccine also started off with lower antibody levels before the booster compared with mRNA vaccine recipients.

Dr. Kirsten Lyke of the University of Maryland School of Medicine, who presented the results at last week’s FDA meeting, cautioned that more data is needed before drawing firm conclusions about boosters.

“This is only antibody data and early immunogenicity data. We do have [T cell] and B cell immune responses that are still being analyzed,” she said at the meeting.

Antibodies are just one aspect of the immune protection offered by vaccination. Memory B cell and T cell responses also play a role in protecting against infection and severe illness.

In addition, Lyke said “we will be following these participants for a full year” to see if there are differences in how long the protection offered by different boosters lasts.

Evidence from the European Union, United Kingdom, and Canada supports mixed dosing during the initial series.

The NIH booster study tested a full dose of the Moderna vaccine. However, in its booster application to the FDA, Moderna requested authorization of a half dose.

Data presented by the company at the FDA meeting last week showed that a half-dose booster also increased the antibody level in people fully vaccinated with that vaccine.

In the end, the FDA authorized a half dose Moderna booster regardless of which vaccine people received initially.

Booster eligibility requirements differ depending upon which vaccine people received initially.

People who are fully vaccinated with Pfizer/BioNTech or Moderna vaccines are eligible for a booster if they are at least 65 years old, or ages 18 to 64 and either at high risk of severe COVID-19 complications due to underlying medical conditions or work-related or institutional exposure.

Fully vaccinated J&J recipients are eligible for a booster at least 2 months after their initial dose.

Dr. Carlos Malvestutto, an infectious disease expert at The Ohio State University Wexner Medical Center in Columbus, said people who have received a single dose of the J&J vaccine should definitely get a booster, given the lower level of protection offered by a single dose of that vaccine.

J&J recipients can choose any brand for their booster, but the mRNA vaccines may offer extra protection.

“You will get a boost in antibody levels [with a J&J booster],” said Malvestutto, “but the boost is much higher if you get an mRNA vaccine.”

In addition to J&J recipients, Malvestutto thinks the benefits of boosters are clearest for people 65 years and older, and people more than 50 years old with underlying medical conditions.

However, “we don’t really see much of a decrease in the level of antibodies in people younger than that, even after 6 months from completing the [initial] series,” he said.

Other eligible people can consider getting a booster if they feel it would benefit them, he said.

Lauren Bryan, RN, an infection preventionist at UCHealth Yampa Valley Medical Center in Steamboat Springs, Colorado, said eligible people should keep in mind that getting a booster can also protect people around them.

“If you meet the criteria for getting a booster because of workplace exposure, consider the impact on you, your co-workers and your family if you develop a breakthrough infection with the more virulent Delta variant,” she said.

If the CDC director signs off on mix-and-match boosters, people eligible for a booster of their initial vaccine would also be able to seek out a booster of another authorized vaccine.

This could decrease demand for the J&J vaccine, which has shown a lower effectiveness against infection compared to the mRNA vaccines.

However, people concerned about rare heart-related side effects — myocarditis and pericarditis — linked to the Moderna and Pfizer/BioNTech vaccines may decide to switch to J&J for their booster.

Mix-and-match boosters will also provide vaccination sites with greater flexibility during the booster rollout.

“In the hospital, we are fortunate to have access to all of the approved vaccines,” said Bryan, “but in lower resource areas or for public health outreach, having the ability to safely mix vaccine brands may allow for better accessibility.”

The overall goal of the booster program is to restore immune protection in fully vaccinated people.

However, Malvestutto said, although there is some waning of protection in vaccinated people over time, people who have not received any doses, especially people with underlying health conditions, are often at greater risk of COVID-19.

“We should not lose sight of the fact that what we need to do is vaccinate the large proportion of people who are still unvaccinated,” he said. “That’s who I see in the hospital every day, that’s who gets admitted with COVID-19.”