Even partial protection of one dose could be enough to slow the spread of the virus, the UW Medicine researchers argue in a paper.

MEDIA CONTACT: Susan Gregg - 206.616.6730, sghanson@uw.edu

Giving one dose of the COVID-19 vaccines currently approved in the United States could curtail the spread of the SARS-CoV-19 in the community more quickly than the recommended two doses, say two vaccine experts at the University of Washington School of Medicine.

In an editorial published today in the Annals of Internal Medicine, Dr. Ruanne Barnabas, associate UW professor of global health, and Dr. Anna Wald, professor of epidemiology and laboratory medicine and pathology, argue that providing partial protection against the virus with just one dose to many people could be more effective in bringing the pandemic to an end than providing more complete protection to a smaller number of people.

Currently the Food and Drug Administration (FDA) has authorized emergency use authorization of two vaccines. Both were approved on the basis of clinical trials in which two doses were given three to four weeks apart.  Both vaccines, one developed by Pfizer-BioNTech and one by Moderna, were highly effective, preventing COVID-19 illness in more than 90% of those who received two doses.

But data from these trials also suggest that a single dose provides more than 50% protection – 52% with the Pfizer-BioNTech vaccine and 51% with the Moderna vaccine, within two to three weeks of injection. 

“This substantial efficacy,” Barnabas and Wald note, meets the FDA’s the requirement that a COVID-19 vaccine should have 50% efficacy to be approved. What’s more, that efficacy is likely to improve as the immune response to the vaccine matures with time, they add.

Despite the surging number of COVID-19 cases and deaths nationwide, vaccine distribution has been slow. To date, only about 3 million doses of vaccine have been shipped in the United States, with another 3 million being held back to assure a sufficient supply for a second dose.

“Since additional vaccine supply is expected, a second vaccine dose could be provided eight to 12 weeks after the first dose to ensure a durable vaccine response,” Barnabas said.

In their paper, Barnabas and Wald argue adopting a single-dose strategy could immediately double the number of doses available, and an expanded one-dose program would, with widespread distribution, stop the virus' spread in communities sooner than the current strategy. 

“A single-dose SARS-CoV-2 vaccine approach deals directly with the shortage of vaccines by vaccinating twice the number of people while maximizing the probability of achieving herd immunity,” they write. 

Reduced-dose strategies have been shown to save lives during other epidemics, they note, in particular during a 2016 yellow fever outbreak in the Democratic Republic of Congo in which reduced-dose vaccines increased the number of people receiving vaccination and saved lives.

Although the FDA has approved the drugs only for the two-dose regimen, public health authorities can override FDA regulations when warranted, the researchers note.

“We agree that the 2-dose regimen in the initial clinical trials was preferable as the possibility for protection after immunization had to be demonstrated. However, public health bodies have flexibility in their authority to recommend and implement a vaccination program that does not stringently reflect the product label.”

– Written by Michael McCarthy

See original story in UW Medicine Newsroom.

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