Additional Covid-19 vaccine booster shots are not needed for the general population, leading scientists said in an article published in the Lancet medical journal on Monday.
The scientists, including two departing senior US Food and Drug Administration officials and several from the World Health Organisation (WHO), said more evidence was needed to justify boosters.
They said current evidence continues to show high protection from vaccines against severe disease.
"Any decisions about the need for boosting or timing of boosting should be based on careful analyses of adequately controlled clinical or epidemiological data, or both, indicating a persistent and meaningful reduction in severe disease," the scientists wrote.
The risk-benefit evaluation should consider the number of severe Covid-19 cases that boosting would be expected to prevent, and whether it is safe and effective against the current variants, they said.
"Current evidence does not, therefore, appear to show a need for boosting in the general population, in which efficacy against severe disease remains high," the scientists wrote.
In the future
The article's authors included the FDA Office of Vaccines Research and Review Director Marion Gruber and Deputy Director Phil Krause, both of whom plan to leave the agency in the next several months, along with WHO top scientists Soumya Swaminathan, Ana-Maria Henao-Restrepo and Mike Ryan.
They acknowledged that some individuals, such as those who are immunocompromised, could benefit from an additional dose.
Broader use of boosters may be needed in the future if there is waning immunity to the primary vaccination or if new variants evolve so that the vaccines no longer protect against the virus, they said.
Boosters could also prove risky if introduced too soon or too frequently, the scientists wrote.
"Current vaccine supplies could save more lives if used in previously unvaccinated populations," the authors wrote.
A panel of experts that advises the FDA on vaccines plans to meet on September 17th to discuss additional doses of the Pfizer /BioNTech shot, the first step in a wider booster roll-out.
Some countries, including Israel, have already begun Covid-19 booster campaigns.
The US government plans to begin offering another round of shots to many fully vaccinated Americans as soon as next week, contingent on approval from health regulators.
As Covid-19 cases caused by the Delta variant of the virus rise, President Joe Biden's administration is concerned that infections among those already vaccinated are a sign that their protection is waning and has pushed boosters as a way to rebuild immunity.
The WHO has argued that the vaccines are still needed for first doses around the globe.