The US Food and Drug Administration (FDA) is preparing to allow "mix and match" coronavirus vaccine boosting, in which people get a different additional shot to the dose they initially received, US media reported.
Citing sources familiar with the situation, the New York Times said the FDA might make the announcement on Wednesday when it is also expected to authorize boosters for the Moderna and Johnson & Johnson vaccines.
A preliminary study released in the United States last week showed that people who have received the J&J vaccine may benefit from a booster dose of a different, messenger-RNA vaccine such as Pfizer or Moderna.
But multiple reports quoted people familiar with the discussions as saying one shot may not be recommended over another, and the FDA could say using the same vaccine is preferable when possible.
"People should generally get the same vaccine as their initial series," a federal official told the Washington Post.
Proponents of mixing and matching point to its benefits in terms of simplifying vaccine rollout, and ensuring those who need boosters can get them regardless of which jab they initially had.
"From a public health perspective, there's a clear need in some situations for individuals to receive a different vaccine," Amanda Cohn, a high-ranking Centers for Disease Control and Prevention official, told the New York Times.
In July the World Health Organization's chief scientist Soumya Swaminathan said mixing and matching vaccines was "a bit of a data-free, evidence-free zone."
The US study on boosters, which has not yet been peer-reviewed, has several limitations.
The number of participants was small, and the immune response could evolve beyond the 15 days observed during the study.
In the United States, over-65s, adults with high-risk medical conditions, and those in jobs where they are frequently exposed to the virus are eligible to receive booster shots.
The World Health Organization's vaccine advisers recommended last week that people with weakened immune systems should be offered an additional dose of all WHO-approved Covid-19 vaccines.
But the WHO wants a moratorium on booster doses for the general population until the end of the year to prioritize first doses in the dozens of nations starved of vaccines.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)