WASHINGTON (BLOOMBERG) - The US Food and Drug Administration (FDA) is leaning towards authorising half-dose booster shots of the Moderna Covid-19 vaccine, satisfied that it is effective in shoring up protection, people familiar with the matter said.
The authorisation would set the stage to further widen the US booster campaign after earlier authorisation of the Pfizer-BioNTech shot.
About 170 million fully vaccinated people in the United States received the Moderna or Pfizer shots, or 92 per cent of the total inoculated so far.
The people spoke on the condition of anonymity, before a potential announcement. It is not clear when an announcement will come.
Any authorisation would also introduce different dosage levels for boosters. Moderna's initial inoculations contained 100 microgram (mcg) doses, and the company's submission to regulators amounted to a push to authorise a half-dose booster, which would allow Moderna to produce more.
Pfizer's shot, in comparison, has 30mcg initial doses and a 30mcg booster.
Moderna declined to comment on Tuesday night (Sept 28). The White House and the FDA also declined to comment.
The US is rolling out boosters to head off what President Joe Biden's health advisers warn are a pair of concerning trends: hints that vaccine efficacy wanes over months, and that the two-dose regiments are weaker generally against the Delta variant of the coronavirus.
America has dealt with a summer and fall wave of new cases, hospitalisations and deaths, driven by spread among unvaccinated people but increasing the exposure risk for the vaccinated.
The FDA had been seeking information about the effectiveness of a full third dose of the Moderna vaccine, but is now ready to move forward and consider the half-dose booster Moderna has proposed, the people said.
Mr Biden, who received his Pfizer booster on Monday, has said this remains a pandemic of the unvaccinated.
Dr Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, has said he believes Pfizer and Moderna will eventually be considered three-dose vaccines.
As the vaccination campaign widens, sites that administer them will have to juggle different versions. In addition to Moderna potentially adding a half-dose booster, Pfizer is seeking authorisation of a vaccine for children aged five to 11, with a 10mcg dose - one-third the strength given to those 12 and up.
Dr Fauci has indicated that there will be progress soon on booster shots for Moderna as well as Johnson & Johnson's one-dose vaccine.
"I believe it will be weeks and not months," he told NBC's Meet the Press earlier this month.