There are about 1.4 million active duty military servicemembers in America. One month ago, some 500,000 of them had received a single dose of a COVID vaccine. Fast-forward to today and the number stands at 775,500.

So what’s led to this turnaround? One critical element has been pressure on the Biden administration to get vaccination numbers up within the federal government as it pitches a mass immunization plea to the public. In the past few weeks, the military opened up COVID vaccinations to all servicemembers and not just those who were among the special tiers.

That’s the key driver of the vaccination boom in the military. But the nuances of vaccine skepticism play a large role here. For instance, studies have shown the Black servicemembers are more hesitant than others to immediately get vaccinated, and younger people just don’t think they have to. There are also vaccine discrepancies within the various arms of the military.

“Between the four military branches, the Army had the lowest rate of vaccination,” according to the Military Times. “Marines were 52% more likely to get vaccinated than soldiers. Sailors and airmen were respectively 45% and 15% more likely.”

The spotty data around servicemembers’ vaccination rates is a political, and public health, headache for the Biden administration as it tries to get millions more Americans their COVID shots. If a soldier is administering a shot to you at a mass vaccination site refuses to get one themselves, there’s plenty of opportunity for mixed messages.

That means the surreal growth in vaccination rates in the military is a welcome sign. The question is whether it’s durable. Red tape may have been keeping certain servicemembers from getting their COVID vaccine if they wanted one. But what matters will be convincing the true hold-outs and skeptics to become immunized.