About 68% of active duty service members have received at least one dose of COVID-19 vaccine, but officials are concerned about threats from the delta variant, Pentagon officials said Wednesday, according to The Hill.

When active duty are combined with reserve and Guard troops, a total of 51% of military personnel have had at lease one dose. The Navy has a 77% vaccinate rate among active duty sailors. The Marine Corps has the lowest rate at 58%.

“We are particularly concerned with the impact of the delta variant on our unvaccinated or partially vaccinated population and its potential spread at installations that are located in parts of the country with low vaccination rates,” Terry Adirim, the acting assistant secretary of defense for health, said.

DOD leaders have been encouraging the vaccines but have not made them mandatory because the Food and Drug Administration has only approved them for emergency use.

Navy photo by Mass Communication Specialist Seaman Jackson Adkins