Some Americans who received COVID-19 vaccines made by Moderna or Pfizer have sought additional Pfizer shots, a move physicians are advising against, Tampa, Fla.-based ABC affiliate WFTS-TV reported Oct. 11.
Because Americans usually don't have to present medical paperwork to get a COVID-19 vaccine, some who have been fully vaccinated are pretending to receive initial vaccinations from a different drugmaker, either because they are worried their vaccination isn't providing strong enough protection or they feel left in the dark about when they will be eligible for a booster.
However, physicians and public health experts are warning against mixing COVID-19 doses, as there is no safety or efficacy data on the practice.
"The biggest concern of course is that we never studied that and so there's no indication that if you get the Moderna shot, you’re going to boost what Pfizer already did. And so essentially instead of acting like a booster, it acts like a different shot. Almost as if you got vaccinated by something different," Jill Roberts, PhD, an epidemiology professor at the University of South Florida in Tampa, told the station.
Mixing doses also makes it difficult for researchers to track vaccination data accurately, Dr. Roberts said.