Study shows mixing and matching booster shots is safe and effective, FDA to discuss this week

A U.S. Food and Drug Administration advisory committee will begin meeting Thursday to discuss whether to approve Moderna and Johnson & Johnson's booster shots. 

A new study by the National Institute of Health released Wednesday shows that people who originally got a Johnson & Johnson shot might get more protection from a Pfizer or Moderna booster. 

"What we’re really talking about is people who got J & J, if they need a second dose, if they should get one of the mRNA vaccines, either Pfizer or Moderna," said Dr. George Rutherford, Chief Infectious Disease Epidemiologist at UCSF. 

The small study, which has not been peer reviewed yet, looked at people who got one Johnson & Johnson shot, and compared their increase in antibodies when they got a booster from either Pfizer, Moderna or another Johnson & Johnson shot.

"In this article, when you boosted with Moderna it went up something like 76 fold, with Pfizer it went up 39 fold and if you gave a second J & J it went up 4 fold," said Rutherford. 

This is the first study looking at mixing and matching booster shots in the US, but Rutherford pointed out that it only measures antibodies – not protection from the virus or symptoms of clinical disease. 

The FDA will look at this data when making their decisions during a two-day session Thursday and Friday. A committee with the Centers for Disease Control and Prevention will then examine the data on its own. 

Rutherford said in the UK, they've been doing a similar mix of shots, giving Pfizer boosters to people who originally got the AstraZeneca vaccine. He said San Francisco's Department of Public Health has also been offering Pfizer boosters to people who got Johnson & Johnson to "try to anticipate the need."

Mixing and matching booster shots would make it easier for people to schedule a booster, but Rutherford said the FDA really has to decide whether that level of increased protection is necessary.

"You know we’re trying to bump immunity from 92% to 95%. Is that really worth 250 million doses of vaccine or whatever the number is?" said Rutherford.

Another question the FDA must answer is whether people who got Moderna shots need a booster at all, since the first two shots are proving to still be effective. 

"Moderna hasn’t shown the same kind of waning phenomena that Pfizer has, but it does wane a little bit," said Rutherford.

Still, the FDA is expected to approve a Moderna booster shot. The recommendations will likely be similar to the Pfizer booster shot's recommendations and only be for people 65 and older, those with underlying health conditions and employees who have a job that raises their risk of exposure to COVID.