(CNN) -- The Pentagon is mandating that US military service members get fully vaccinated against Covid-19 immediately, after the Food and Drug Administration fully approved the Pfizer/BioNTech coronavirus vaccine this week.
"After careful consultation with medical experts and military leadership, and with the support of the President, I have determined that mandatory vaccination against coronavirus disease 2019 (COVID-19) is necessary to protect the Force and defend the American people," Secretary of Defense Lloyd Austin wrote in a memo released Wednesday.
He added, "To defend this Nation, we need a healthy and ready force."
The Pentagon previously said that Austin would likely take this step once one of the Covid-19 vaccines received full authorization from the FDA. On Monday, the FDA granted full approval to the Pfizer/BioNTech Covid-19 vaccine, which is the only Covid-19 vaccine thus far that has received full authorization by the FDA.
In his memo, Austin said he is directing the Military Department services to "immediately begin full vaccination" of all Armed Forces members or in the Ready Reserve, including the National Guard, who are not yet fully vaccinated.
Austin said the Secretaries of the Military Departments "should impose ambitious timelines for implementation" and "will report regularly on vaccination completion."
The defense secretary sent the memo Tuesday to senior Pentagon leaders, commanders of the Combatant Commands and Defense Agency and Defense Department Field Activity Directors.
On Wednesday, Pentagon press secretary John Kirby said that 68% of the active duty forces is fully vaccinated, with an estimated more than 76% have received the first dose of the Covid-19 vaccine.
"The secretary has made clear his expectation to the military departments that he wants them to move with some alacrity here and get the force fully vaccinated as fast as possible," Kirby told reporters.
For now, this mandatory vaccine will just be Pfizer, and "we'll see where it goes with the other licensures," he said.
Service members actively participating in Covid-19 vaccine clinical trials, or with religious reasons, or with a preexisting condition and advised by a doctor not to receive the vaccine will be exempt from the mandate.
Asked about service members who refuse to receive the vaccine, Kirby said the individual will have the opportunity to sit with a physician and their military leadership "to talk about the risks that their objection will impose on the unit and on the force and on their teammates."
Commanders are expected to use "a wide range of tools" to help "these individuals make the right decision" short of having to take disciplinary action, Kirby said.
"It's a lawful order. We fully anticipate that our troops are going to follow lawful orders," he said. "When you raise your right hand and take that oath, that's what you agree to do. "
President Joe Biden had announced late last month that he was ordering the Pentagon to "look into how and when" it will add the Covid-19 vaccine to the list of mandatory military vaccinations.
If one of the vaccines did not receive full authorization by mid-September, Austin had planned to ask Biden for a waiver to make it mandatory for all US service members to receive the vaccine.
Other coronavirus vaccines, Moderna and Johnson & Johnson, had been authorized for emergency use in the US.
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