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Photo: Justin Tallis/Pool/Getty Images

U.S. health officials have begun a clinical trial with adults fully vaccinated against COVID-19, administering a booster shot of a different vaccine brand to the one they've already received, the National Institutes of Health announced Tuesday.

Why it matters: The study will examine immune responses and the safety of mixing different vaccines. Scientists will also measure the shots' efficacy in staving off emerging variants, according to a statement from the NIH.

  • Per a statement from NIAID director Anthony Fauci: "Although the vaccines currently authorized by the U.S. Food and Drug Administration offer strong protection against COVID-19, we need to prepare for the possibility of needing booster shots to counter waning immunity and to keep pace with an evolving virus."
  • If booster shots are required, this study could help health officials decide which vaccine combinations are best.

Details: The study will examine 150 volunteers who've received one of the three COVID-19 vaccines authorized for use in the U.S. — Johnson & Johnson's, Moderna's and Pfizer-BioNTech's.

  • Each vaccine group will have enrolled some 25 people between the ages of 18 and 55 and about 25 people in the 56 years and older age group.
  • "Twelve to 20 weeks following their initial vaccination regimen, participants will receive a single booster dose of the Moderna COVID-19 vaccine as part of the trial," according to the NIH.
  • Another aspect of the study will see volunteers who've yet to receive a coronavirus vaccine enrolled. Initially, they'll receive the two-dose Moderna vaccine before receiving a booster dose of a vaccine about 12 to 20 weeks later. 

The big picture: Research indicates that all three vaccines authorized for use in the U.S. protect against variants, to varying degrees.

  • The Public Health Agency of Canada updated its coronavirus vaccine guidance on Tuesday to permit Canadians to receive a different dose for their second shot, though it still recommends using the same brand.
  • Health officials in the United Kingdom are expected to release initial results this summer of a clinical trial testing the effectiveness of mixing COVID-19 vaccines.

Go deeper: Vaccine boosters could be necessary as soon as September

Go deeper

Jun 1, 2021 - Health

WHO approves China's Sinovac COVID vaccine for emergency use

A healthcare worker administers a dose of Sinovac's vaccine to an elderly man at a mall theatre converted into a vaccination center in San Juan, Metro Manila, Philippines. Photo: Ezra Acayan via Getty Images

The World Health Organization said Tuesday it has approved the Sinovac COVID-19 vaccine for emergency use for adults over 18, making it the second Chinese-developed shot given the green light.

Why it matters: The approval will allow Sinovac to join COVAX and distribute its vaccines to developing countries. The global vaccine distribution initiative currently faces "major supply problems" due to restrictions on Indian exports, Reuters reports.

Jun 1, 2021 - Health

Moderna applies for full FDA approval of COVID-19 vaccine

Maryland National Guard Brigadier General Janeen Birckhead visits with a woman as she receives her Moderna coronavirus vaccine from Specialist James Truong (L) on May 21 in Wheaton, Maryland. Photo: Chip Somodevilla/Getty Images

Moderna is seeking full approval from the Food and Drug Administration for its coronavirus vaccine, the company announced Tuesday.

The big picture: Obtaining a Biologics License Application (BLA) from the FDA requires at least six months of data, unlike the two months of data required for emergency use authorization from the agency.