WASHINGTON (SBG) — Millions of Americans who are now eligible for COVID-19 booster shots are wondering whether they should stick with the same vaccine or switch to a different shot after U.S. regulators approved mixing and matching.
Mixed messages from public health agencies have made the decision even more confusing. Last week, the Food and Drug Administration and Centers for Disease Control and Prevention said qualifying individuals could boost with either the Pfizer, Moderna or Johnson & Johnson shots regardless of their original vaccine.
The CDC and FDA largely left it up to individuals to decide whether to stick with the same vaccine or switch to something different. On Friday, CDC Director Rochelle Walensky estimated that "the vast majority of people" would likely select the shot they originally received but said the recommendations allowed for flexibility.
The head of the National Institutes for Allergies and Infectious Disease Dr. Anthony Fauci appeared to contradict that guidance, suggesting that people ought to stick to the same regimen.
"We would hope that people, if available, would get the boost from the original product," Fauci told ABC "This Week" Sunday. "But, if not, there's the flexibility of what we're calling mixing and matching." On Friday, Fauci told CNN that it was "generally recommended" that people boost with the same vaccine.
Currently, the data on mixing and matching vaccine is limited, making it more difficult for health care providers and pharmacists to provide strong recommendations on which shot to get.
The FDA and CDC based their decision largely on a study sponsored by the National Institutes of Health that looked at safety and immune response in people who receive different COVID vaccines. The study did not look at efficacy per se.
Across the board, the study indicated a Moderna booster (at 100 micrograms) produced the biggest increase in neutralizing antibody titers.
The effects were the strongest among people who had received just one dose of the Johnson & Johnson. According to the study, J&J recipients boosted with Moderna saw antibody levels rise 76-fold in 15 days, compared with a fourfold increase after an additional J&J dose. The Pfizer shot produced a 35-fold increase.
Mixing and matching the mRNA vaccines had a less significant effect. They also had less Pfizer recipients saw antibodies increase 32-fold after receiving Moderna compared to a 20-fold increase after a third Pfizer shot. Recipients got a 12.5-fold boost after J&J.
Moderna recipients who received a boost of J&J saw antibodies increase sixfold, compared to a 10-fold increase after receiving a third dose of Moderna and an 11-fold increase after Pfizer.
The need for boosters followed reports of breakthrough infections and pharmaceutical companies reporting waning efficacy over time. The CDC has estimated J&J's real-world efficacy to be around 60% compared to 95% for Moderna and 80% for Pfizer. Each vaccine remains highly effective in preventing hospitalization and death.
Regardless of the booster, every vaccine produced a significant increase in neutralizing antibodies. However, researchers concluded that those who got a different booster had "as good or higher" neutralizing antibodies than those who received the same vaccine.
With the exception of a double J&J shot, all groups saw increases that have been assopciated with 90% vaccine efficacy against symptomatic COVID-19, according to Dr. Kirsten Lyke, head of the Center for Vaccine Development at the University of Maryland and a co-author of the study.
There were no serious adverse effects related to the booster doses and many of the side effects mirrored first doses, including headache, fever, chills, fatigue and injection site pain.
Dr. Walensky cautioned that the results of the NIH study were based on laboratory tests, not clinical trials. The study involved fewer than 500 participants with results covering just one month. The clinical trials involved thousands of participants over several months. J&J's clinical trials showed up to 94% efficacy against symptomatic COVID following a boost. Pfizer's efficacy reached 96% after a boost and Moderna reported strong results.
It's unclear if there may be real-life benefits to boosting with the same or a different shot.
Walensky told NBC's "Meet the Press" that those potential benefits would be studied in the future. She emphasized that there was no "absolute preference" for choosing one booster over another and that all showed significant clinical benefits.
The greenlight on boosters prompted nearly 13 million people to get additional shots. According to CDC data, there are more people lining up for boosters than for first vaccines.
There are still 64 million eligible Americans who have not yet received a first shot. The Biden administration has emphasized that the U.S. has adequate supply to cover those individuals plus the booster campaign and shots for children. The FDA is scheduled to vote on approving the Pfizer vaccine for 5-11-year-olds Tuesday.