It is clear now that immunosuppressed populations, in general, do not produce an adequate immune response after receiving two doses of a Covid vaccine, Fauci said.

Federal health officials are working "as quickly as possible" to authorize a third Covid-19 vaccine shot for Americans with weakened immune systems, White House chief medical advisor Dr. Anthony Fauci said Thursday.

It is clear now that such people – including cancer and HIV patients or those who have had organ transplants – in general do not produce an adequate immune response after receiving two doses of a Covid vaccine, Fauci said.

"Immunocompromised individuals are vulnerable," Fauci said during a White House briefing. "It is extremely important for us to move to get those individuals their boosters, and we are now working on that and we will make that be implemented as quickly as possible. ... It is a very high priority."