A large number of U.S. Marines are choosing not to receive a vaccine for COVID-19, CNN reported.

About 40 percent of Marines who have been offered a shot, or 48,000, have so far declined a vaccine to protect against the coronavirus. Of the 123,500 Marines who have been offered a vaccine, about 75,500 agreed to get one, according to data obtained by CNN.

Over 100,000 Marines have yet to be offered a vaccine, the network said.

“We fully understand that widespread acceptance of the Covid-19 vaccine provides us with the best means to defeat the pandemic. The key to addressing the pandemic is building vaccine confidence,” Marine Corps spokesperson Col. Kelly Frushour said in a statement to CNN.

Marines might decline COVID-19 vaccines for several reasons, Frushour said. They might prefer others to receive priority for it or are choosing to wait until it’s institutionally mandated. They could also be allergic or have already secured a vaccine through other channels, CNN reported.

“Servicemembers who decline one day can change their mind and become vaccinated when next the opportunity presents itself,” Frushour added.

The Marine Corps did not immediately return a request for comment from Insider.

In February, a top Pentagon official said about a third of all U.S. troops had at the time refused to get a COVID-19 vaccine.

“Acceptance rates are somewhere in the two-thirds territory,” Air Force Maj. Gen. Jeff Taliaferro, the Joint Staff’s vice director for operations, told the House Armed Services Committee during a hearing on the Defense Department’s response to the pandemic.

The vaccine is not compulsory for servicemembers, but Taliaferro told Rep. Mike Rogers, the top Republican lawmaker on the committee, that the military must do better “to help them understand the benefits.”

The military’s acceptance rate at the time, however, was higher than that of the general population. According to the Kaiser Family Foundation, general population vaccination rates hovered around 50 percent at the time Taliaferro made his remarks earlier this year.

The coronavirus has infected more than 31 million people in the United States, according to data compiled by Johns Hopkins University. More than 561,000 Americans have died from it. About 19 percent of the U.S. population has been fully vaccinated so far, Johns Hopkins data says.

This article was written by Yelena Dzhanova and originally published on the Insider.