What you need to know about ‘mix-and-match’ COVID-19 vaccine boosters
The Centers for Disease Control and Prevention officially endorsed and recommended booster shots for all three brands of the COVID-19 vaccine Thursday. At the same time, the new CDC guidance allows recipients to “mix and match” their original vaccine brand with a booster of their choice.
The CDC announcement follows a Food and Drug Administration authorization Wednesday that also allowed the use of coronavirus vaccine booster shots that do not match an individual’s initial brand.
Here are six things you need to know about mixing or matching your booster shots:
What does this authorization mean right now?
Now that both the FDA and CDC have fully approved of Johnson & Johnson, Pfizer-BioNTech and Moderna vaccine booster shots for millions of Americans, eligible people can begin getting a booster shot as early as Friday.
Both agencies also authorized mixing vaccine brands between one’s original series and booster shots. For example, a person who originally received a J&J vaccine can now get a booster with mRNA technology, Moderna or Pfizer.
People who originally received a mRNA vaccine are eligible for a booster shot if they are 65 years and older or “vulnerable” to COVID-19. Vulnerable may mean you live in a long-term care facility, work in a high-risk location, or have underlying condition such as a chronic lung disease or obesity.
All adults who originally received a J&J vaccine, however, are eligible for a booster shot.
Since mid-August, the U.S. has been administering third Moderna and Pfizer doses to a small group of patients who are moderately to highly immunocompromised, including organ transplant recipients, some cancer patients and folks who take certain immunosuppressant medications. But this has only affected people with a very narrow list of conditions. The third doses serve a different purpose from booster shots, which are being administered to a wider base of people.
What does the authorization mean for each type of vaccine recipient?
For those who initially received the Moderna or Pfizer vaccine, officials said one generally should stick with the same vaccine series, primarily because there is no evidence of marked benefits, though the FDA announcement made no recommendation to that effect.
Some reasons to switch to a different brand might be if the individual had a particularly bad reaction to the mRNA technology included in both Moderna or Pfizer vaccines or if availability of their initial series is limited. A preliminary study discussed by an FDA advisory committee showed switching would be all right if the initial brand isn’t currently available.
However, for those who took the one-dose J&J vaccine, early research suggests taking the Moderna vaccine as a booster yielded the greatest antibody increase. The study showed that a second shot using the Moderna vaccine triggered a 76-fold increase in antibody levels. By contrast, a Pfizer booster increased antibody levels 35-fold, and the coordinating J&J booster yielded only a fourfold increase.
“If the FDA recommends mix and match, then I think the most promising thing is that people who’ve got the J&J would have the ability to switch over to Moderna or Pfizer for their boosters,” Tanna said.
Safety concerns may also play into some J&J recipients’ decision to switch to an mRNA booster shot. According to Yale Medicine, out of 9 million doses administered by May, 28 people developed a rare blood clotting disorder, three of whom died. The side effect tended to be slightly more common in women under 50 years old.
In July, the FDA also attached a warning for a rare neurological condition called Guillain-Barre syndrome to the J&J vaccine. Again, the cases were exceedingly rare with about 100 suspected cases primarily among men age 50 years and older.
How conclusive is the study the FDA committee is basing their authorization partially on?
The study that shows mixing brands may be beneficial is “encouraging,” but is by no means conclusive, according to Tanna. The results of the study have yet to be formally peer reviewed and published. It is currently in preprint form, a version of a scientific study posted publicly prior to formal peer review.
Tanna pointed out a few caveats to keep in mind for the study. The number of people who participated in the study was relatively small, with about 50 people receiving a specific combination of original series and booster.
The study was also conducted before the Delta variant became the dominant strain of COVID-19, Tanna said. Additionally, the study primarily looked at antibody counts, which are a good measure of general resistance; however, it didn’t look at the T-cell response, which is harder to measure but is indicative of how well a vaccine limits the severity of the illness.
“The study wasn’t necessarily powered to say that one vaccination strategy of mixing and matching is better than another. And I think that’s what we all want, right?” Tanna said. “Tell me which ones to get, so I have the most protection, and I don’t think we can draw those conclusions just yet.”
How does this authorization affect different age groups?
The FDA authorized Moderna half-dose booster shots Thursday for those 65 and older or vulnerable people, which may be administered six months after the first set of doses. They also authorized a J&J booster for all adults.
The agency’s authorization makes it so that anyone 18 and older who initially received the J&J vaccine can get any other brand of booster vaccine only two months after their single dose.
The agencies’ announcements stressed that there is no need for recipients of one of the mRNA vaccines to get a booster if they are younger than 65 and do not qualify as vulnerable to the disease.
Is vaccine supply a concern?
In a way, yes. The country and each state likely has a deep stockpile of vaccine, even as the rest of the world struggles with shortages. However, the concern lies in which vaccines are available and where. Those who are unable to find a booster near them that corresponds with their original series, based on the new authorization, would be able to switch to a vaccine that is more readily available.
The interchangeability is expected to be particularly useful in nursing homes and other institutional settings where residents have received different shots over time.
Tanna said that, in her experience, all of her patients who are eligibly for the Pfizer booster have been able to find one easily and within the area.
Are the boosters a full or half-dose?
This is where the data gets confusing and a decision more difficult. The authorized Pfizer booster shot is one full dose of the vaccine.
The Moderna booster, on the other hand, is only recommended as a half-dose of the original full shot. The study that suggests a Moderna booster may provide a 76-fold increase in antibody levels when mixed with a J&J vaccination used a full-strength dose as a booster. It is unclear if the half-dose of Moderna that the FDA authorized would provide the same result without further testing, Tanna said.
Tanna said she is hopeful that this authorization will provide some much needed clarity and guidance for those who initially received the J&J vaccine.
“All these recommendations that have been made for additional doses or for booster vaccinations, the people who got Johnson and Johnson have felt left behind, especially if they’re high risk, and they really haven’t had the guidance they need,” Tanna said.
