The Marines' vaccination rate, 94 percent, is the lowest among the military, raising questions about what it means for safety and readiness for the branch that is often the US's first line of defense.
The Navy, in comparison, has a 99.7 percent vaccination rate ahead of the same Sunday deadline.
It is unclear what the future holds for Marines who refuse the jab.
``We will be addressing each case on a case-by-case basis is what we’re going to be doing,' Secretary of the Navy Carlos Del Toro said last week.
'We’re just not going to kick them out on the day of the deadline itself.'
Active duty Marines have until Sunday to get vaccinated, while reservists have until December 28.
In the Army, 95 percent of soldiers have received at least the first dose. Active-duty soldiers have until December 15 to be fully vaccinated, with the Army announcing that those who refuse will not be allowed to reenlist or be promoted.
The Office of Management and Budget stated Wednesday that 92 percent of federal government workers, including the military, have been vaccinated, with just four percent being granted religious or medical exemptions.
According to the Washington Post, marines are younger on average than members of other services, are mostly male and generally don't have college degrees, all of which are tied to lower rates of vaccination in the US.
Analysts also point to the spread of fake news about the vaccine, political and societal attitudes and the culture of each branch of the military as reasons why members are holding out.
Earlier this month, Commandant David H. Berger and his senior enlisted adviser, Sgt. Maj. Troy E. Black, released a video message calling for Marines to get the jab.
'When something bad happens around the world and the president says, "I need to know how long it’s going to take to get Marines there," it’s too late then to get vaccinated,' Berger said.
'It’s challenging for us to be able to continue the mission if we’re not ready to go,' Black added.
Berger pressed: 'We need every single Marine in the unit to be vaccinated. We don’t have extra Marines. We’re a pretty small force, and we have to make sure that everybody on the team is ready to go all the time. That’s our job.'