Health care providers in the United States should stick to the two-dose schedule for both authorized COVID-19 vaccines, the Food and Drug Administration said in a statement this week. Some experts have suggested that delaying the second dose could stretch limited quantities of the vaccines further.
Any dose adjustments could be evaluated in clinical trials, FDA Commissioner Stephen Hahn and Peter Marks, the director of the Center for Biologics Evaluation and Research, said in a statement. “However, at this time, suggesting changes to the FDA-authorized dosing or schedules of these vaccines is premature and not rooted solidly in the available evidence,” they said.
Moderna’s COVID-19 vaccine takes two doses given 28 days apart, and the Pfizer / BioNTech COVID-19 includes two doses given 21 days apart. Data from the clinical trials suggested that people had some protection against COVID-19 after the first shot, but the trials were not designed to test if only one dose worked. Still, the evidence was enough for some experts to say that we should get a first dose to as many people as possible, and then give a second shot when more supply is available.
The United Kingdom, which is currently battling a frightening COVID-19 surge driven by the more-contagious coronavirus variant, is taking that approach. Health authorities there said that people should delay the second dose for up to three months. More controversially, they’re also allowing providers to mix-and-match vaccine brands in some circumstances — someone could get a first shot of Moderna and a second shot of Pfizer, if it’s the only one available.
One concern in delaying a second dose is that a single shot could give only partial immunity. Without a subsequent booster to lock in protection, the virus could still infect people who have only gotten one shot and could hypothetically mutate into forms that escape the vaccine. “You are essentially maximizing the opportunity for the virus to learn about the human immune system,” Paul Bieniasz, a virologist at Rockefeller University in New York, told Stat News.
Sudden changes to vaccine recommendations could also shake fragile public trust in the COVID-19 vaccine.
The FDA statement should settle the debate in the US for the time being. “We know that some of these discussions about changing the dosing schedule or dose are based on a belief that changing the dose or dosing schedule can help get more vaccine to the public faster,” Marks and Hahn said in their statement. “However, making such changes that are not supported by adequate scientific evidence may ultimately be counterproductive to public health.”
Right now, the limiting factor for vaccination in the US isn’t doses — it’s the delivery of those doses. Over 15 million doses of the COVID-19 vaccines have been distributed, but only 4.5 million people have gotten their first dose. Making more doses available won’t solve the current problem of getting shots in arms. The rollout has been slower than promised — the federal government left state and local health departments to figure out the logistics of vaccination programs, and the process has been inconsistent and confusing for both patients and health care providers.