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This fact brief was originally published as an experiment to test the concepts behind fact briefs.

Readers should be aware that while there is still a lot of useful information in fact briefs like this one, not all of them reflect Gigafact's current methods and standards for fact briefs. If you come across any that you feel are out of date, don't hesitate to contact us at support@gigafact.org.

FACT BRIEF

Does available data support delaying second doses of the two-dose COVID-19 vaccines in order to give more people a first dose?

Wednesday, February 3, 2021

By Mia Dillon

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Data is too limited to determine if delaying the administration of the second dose of two-dose COVID-19 vaccines reduces their efficacy.

The first two vaccines authorized by U.S. authorities are given in two doses, three weeks apart in the case of the Pfizer-BioNTech vaccine and four weeks in the case of the Moderna vaccine. The Centers for Disease Control says the second dose may be administered up to six weeks after the first if circumstances require.

The U.K. decided to delay administering the second dose by up to 12 weeks, in an effort to get the first dose to more people more quickly after identifying a more contagious variant of the coronavirus. Scientists say that move was not grounded in data. “It is important to note that there is very little empiric data from the trials that underpin this type of recommendation,” said Dr. Joachim Hombach of the World Health Organization.

This fact brief is responsive to conversations such as this one.

Sources

Centers for Disease Control: Interim clinical considerations for use of mRNA COVID-19 vaccines

Food and Drug Admnistration: Statement on following the authorized dosing schedules for COVID-19 vaccines

GOV.UK: Optimizing the COVID-19 vaccination program

World Health Organization: Transcript of Jan. 5, 2021, media briefing (discussion of second doses from p. 14)

Guardian: No data to support UK delay of vaccines’ second dose

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Gigafact

Between 2020 and 2022, under close editorial supervision, Gigafact contracted a group of freelance writers and editors to test the concepts for fact briefs and provide inputs to our software development process. We call this effort Gigafact Foundry. Over the course of these two years, Gigafact Foundry writers published over 1500 fact briefs in response to claims they found online. Their important work forms the basis of Gigafact formats and editorial guidelines, and is available to the public on Gigafact.org. Readers should be aware that while there is still a lot of relevant information to be found, not all fact briefs produced by Gigafact Foundry reflect Gigafact's current methods and standards for fact briefs. If you come across any that you feel are out of date and need to be looked at with fresh eyes, don't hesitate to contact us at support@gigafact.org.

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About fact briefs published on Gigafact

Fact briefs are short, credibly sourced summaries that offer “yes/no” answers in response to claims found online. They rely on publicly available, often primary source data and documents. Fact briefs are created by contributors to Gigafact —a nonprofit project looking to expand participation in fact-checking and protect the democratic process. See all fact briefs here.