Trending Clinical Topic: Single-Dose Vaccination

Ryan Syrek


March 05, 2021

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As vaccination efforts continue to ramp up worldwide, interest in single-dose administrations has increased, leading to this week's top trending clinical topic. Data submitted to the US Food and Drug Administration about the efficacy of a single dose of the Pfizer/BioNTech vaccine, along with previous findings about a single Moderna vaccine dose, have garnered much recent attention (see Infographic below).

A letter regarding the Pfizer vaccine, published in The New England Journal of Medicine, states that "the administration of a second dose within 1 month after the first, as recommended, provides little added benefit in the short term, while high-risk persons who could have received a first dose with that vaccine supply are left completely unprotected." Correspondence published in The Lancet that includes data from Israel showed that one dose of the Pfizer vaccine was associated with 85% protection against symptomatic COVID-19 in an adjusted analysis of more than 9000 healthcare workers.

The duration of protection with a single dose remains unclear, however. At a February 19 White House press briefing, Anthony Fauci, MD, said that the United States would be sticking to the current two-dose strategy for both the Pfizer and Moderna vaccines. "And the reason is, even though you can get a fair degree of protection after a single dose, it clearly is not durable," he said. "We know that the durability is not as much as the durability that you would get with the boost." Fauci and other experts argue that more data are needed before diverting from the regimen that was tested in clinical trials.

Even so, advocates suggest that aggressive strategies may be warranted while vaccine supply is limited. F. Perry Wilson, MD, MSCE, argues that a single-dose vaccination strategy may be appropriate for lower-risk, high-exposure individuals, while the two-dose regimen could be reserved for older adults and other high-risk populations. He says that a booster could then be given to those who received a single dose when supplies are available.

In other single-dose news, new findings suggest that the one-shot Janssen/Johnson & Johnson COVID-19 vaccine reduces the risk for asymptomatic transmission by 74% at 71 days compared with placebo. This comes on the heels of data that showed that adenovirus vaccine provides 85% efficacy globally against severe COVID-19 illness and is 72% efficacious against moderate to severe illness in the United States. Phase 3 results showed that the single-dose vaccine was equally effective, regardless of age, race/ethnicity, absence or presence of comorbidities, and geography. The 44,000-participant ENSEMBLE study was conducted in the United States, South America, and South Africa.

The data supporting the efficacy of the different vaccines are encouraging, especially given the speed with which the vaccines were developed. As Matthew Zahn, MD, said during a February 18 media briefing sponsored by the Infectious Diseases Society of America, although they may have been rushed, all of the necessary scientific and safety steps were taken. As the rush now shifts to vaccinating as many people as possible as quickly as possible, interest in single-dose strategies became this week's top trending clinical topic.

Read more clinical information about COVID-19 vaccines.


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