The FDA and CDC recently announced that previously unvaccinated Americans can now receive only a single dose of the bivalent Moderna or Pfizer mRNA vaccines. To be clear, this is not saying they can choose to have one or two doses and be considered fully vaccinated either way -- only one dose is available to them. The CDC made a related decision in respect to international travelers who fly into the U.S. They "will now be considered fully vaccinated 2 weeks after getting a single dose of either the Pfizer or Moderna mRNA vaccine any time after August 16, 2022, when bivalent formulations first became available." However, a more recent decision from the White House made this announcement moot by eliminating any vaccination requirements for arriving travelers.
In practice, these policy changes will probably not affect many people. The approximately 30% of Americans who have refused all COVID-19 vaccines for over 2 years -- often for political reasons and because of widespread misinformation -- are unlikely to change their attitudes merely because they are now limited to receiving only a single bivalent vaccine dose. And there would have been few international travelers, particularly foreigners, whose only vaccine experience would have been a single bivalent mRNA vaccine. Even so, it's worth exploring what lies behind what just happened.
Since the mRNA vaccines were first rolled out in late 2020, the standard primary series always has been two doses, which remains the legal definition of "fully vaccinated." Indeed, CDC recommends that Americans receive multiple mRNA vaccine doses, either three or four depending on age and health status. Why, then, do FDA and CDC suddenly consider one dose of the bivalent vaccines to be sufficient for unvaccinated people? What data underlie the decisions, and how were those decisions made? The simplest answers are: None and who really knows?
FDA official Peter Marks, MD, PhD, has referred to "simplifying" vaccine administration as being the driver for the recent change and "believes" that allowing unvaccinated people to receive only a single dose will "help encourage future vaccination." Given the reasons behind vaccine refusal, that belief seems quite naïve. Marks also refers to how "most of the U.S. population" has been either infected by the virus, already vaccinated, or both. The unstated implication is that an unvaccinated person now needs only a single vaccine dose to boost immunity conferred by prior infection. Indeed, several science reporters have told me that's what FDA officials are saying in private briefings. While there is solid science behind the hybrid immunity argument, there are also ethical concerns.
I will say again that few unvaccinated Americans will now change their minds -- but some might. However, not all of those mind-changers will have been previously infected, so some will lack any prior immunity. It's not possible to estimate the number of people that fall into this category, but it won't be zero. After all, the FDA is still seeking, rightly, to "encourage future vaccination."
There is literally no data on how well a single dose of a bivalent mRNA vaccine will protect anyone. But we have known for over 2 years that a single dose of the original vaccines was not good enough. The human immune system has not suddenly changed -- I think that giving only a single vaccine dose, of whatever composition, to immunologically naïve people (i.e., no prior infection or vaccination) will leave them perilously under-vaccinated, and hence at future risk of COVID-19. It's particularly problematic if those people believe they are now "fully protected" and increase their exposure to infection. The new one-dose policy is letting these people down.
A better, more humane policy would be to continue to allow every previously unvaccinated person access to two bivalent vaccine doses. Their own knowledge and input from their physicians could guide them as to whether they prefer one dose or two. But they should have the choice -- it's the ethical option.
When flawed policy changes like this one are made, we must ask whether it's appropriate for FDA officials to have that kind of decision-making capacity. In my opinion, FDA has botched several aspects of COVID-19 vaccine policy over the past year. It's time for a shake-up at the agency, particularly with the winding down of any oversight from the White House. "Follow the science" has always been the Biden administration's guiding principle on COVID-19 topics. It should remain so.
John P. Moore, PhD, is a professor of microbiology and immunology at Weill Cornell Medicine in New York City.