The Food and Drug Administration is expected to approve Covid-19 vaccine booster shots this week, according to reports.
The FDA amendment of the emergency use authorisations for the Pfizer and Modern vaccines would allow anyone with compromised immune systems to get a third dose.
The move, which could come as early as Thursday, comes after a panel of advisers to the Centers for Disease Control and Prevention recommended the move in July.
“The FDA is closely monitoring data as it becomes available from studies administering an additional dose of the authorized COVID-19 vaccines to immunocompromised individuals,” said an FDA spokesperson.
“The agency, along with the CDC, is evaluating potential options on this issue, and will share information in the near future.”
The CDC says that around 9m adults in the US are immunocompromised, including organ transplant recipients, cancer patients, those with HIV among others.
A Johns Hopkins study showed that in those groups of patients, a majority of people did not develop antibodies to the coronavirus after vaccination.
The others in the study only developed a low level of protection against the virus.
In the study a third dose of vaccination increased their antibody levels.
The US has seen 36.2m Covid cases during the pandemic and there have been 619,000 deaths caused by the coronavirus.
Next month the White House is expected to lay out a Covid-19 vaccine booster strategy for all vaccinated Americans.
US Surgeon General Dr Vivek Murthy told CNN that the Biden administration was considering who would need booster shots and when they should get them.
“We’ve been concerned about these individuals. We’ve been following them closely, and I think most of us believe that we’ve got to do more to protect these individuals,” he said.