US military troops must immediately begin to get the Covid-19 vaccine, Defence Secretary Lloyd Austin said in a memo, ordering service leaders to impose ambitious timelines for implementation.

More than 800,000 service members have yet to get their shots, according to Pentagon data. And now that the Pfizer vaccine has received full approval from the Food and Drug Administration, the Defence Department is adding it to the list of required shots troops must get as part of their military service.

The memo, which was obtained by The Associated Press, does not dictate a specific timeline for completing the vaccinations. But it says the military services will have to report regularly on their progress.