About 33 percent of service members have declined voluntary coronavirus vaccinations, defense officials said Wednesday, acknowledging that more inoculations would better prepare the military for worldwide missions.

Nearly 150,000 service members are fully vaccinated, a panel of defense officials told lawmakers in a House Armed Services Committee hearing on the Pentagon’s coronavirus response. About two-thirds of troops who were offered the vaccine accepted it. There are about 1.3 million active-duty troops.

The acceptance rate “mirrors preliminary data that we see in other communities” of Americans, Air Force Brig. Gen. Paul Friedrichs, a Joint Chiefs of Staff health official, told lawmakers.

The military is collecting data on race and ethnicity among those who accept vaccinations, Friedrichs said in a discussion about reluctance that some communities have about the vaccine. But the officials acknowledged limitations in what they can do to compel troops to receive vaccinations.

“We need to continue to educate our force and help them understand the benefits [of vaccines] and ensure leadership is involved,” said Air Force Maj. Gen. Jeff Taliaferro, the vice director of operations for the Joint Chiefs.

The military has learned to work in places where coronavirus infections are a reality, he said, but “the addition of the vaccine should make us more capable in that environment.”

The military mandates that service members receive a variety of vaccinations at enlistment, and often additional inoculations are required before deployments for typhoid, polio and other diseases. But the emergency use authorizations for the Moderna and Pfizer-BioNTech coronavirus vaccines prevent commanders from requiring their use without Food and Drug Administration approval, Taliaferro said.

Taliaferro said defense officials don’t know why some troops turn down opportunities to inoculate.

A survey by the military family nonprofit Blue Star Families revealed skepticism about the vaccine within the community.

“I’m not sure I want to be a guinea pig, and I really don’t want my kids to be either,” one military spouse told the group. “I want to know the side effects and what can happen in 20 years.”

The Defense Department has prioritized service members and civilian workers, including those working on the front lines of the pandemic, personnel in strategic positions, and teachers and others working with children.

U.S. service members are healthier and younger than the overall U.S. population, though 21 have died of coronavirus infections, according to Pentagon data.

Infection outbreaks have occurred on 200 Navy ships, derailed training exercises and delaying maintenance on vehicles and vessels, said Rep. Mike D. Rogers (R-Ala.), a member of the committee.

Rogers expressed concern that FDA approval for the vaccine, which would help the Pentagon mandate inoculation, might not arrive until 2023.

“I’m not sure we can wait for two years,” he told the panel.

Rep. Mike Green (R-Tenn.), a former Army physician, said he was concerned about rewriting the statute that prevents the military from requiring troops to receive treatments not approved by the FDA.

The law was put in place because of the Tuskegee study, Green said, a cruel, decades-long experiment that began in the 1930s involving Black men with syphilis. Researchers watched them die untreated and later withheld drugs that could help, such as penicillin.

“We need the full-blown research done before we saddle our warriors with an experimental medication,” Green said.

Dan Lamothe contributed to this report.