The Pentagon is preparing to issue updated guidance to require all US service personnel to be vaccinated after Monday's approval of the Pfizer Inc's Covid-19 vaccine by the Food and Drug Administration (FDA), Pentagon spokesperson John Kirby has said.

According to Reuters, Kirby told a briefing the completion date for vaccine guidance was still being worked on.

The FDA granted full approval on Monday to the vaccine, which had earned emergency-use authorisation in December, making it the first to secure such validation as US health authorities struggle to win over vaccine skeptics.

Asked if similar guidance could be given for other Covid-19 vaccines, Kirby replied: "Right now we're focused on the Pfizer vaccine because of the FDA approval."