Having COVID doesn’t guarantee immunity, study of Marine recruits finds Recruits train aboard Marine Corps Recruit Depot Parris Island, S.C. (Lance Cpl. Devin Darden/Marine Corps) Have you had COVID? Think you’re immune from it in the future? Think again, according to the results of a new study of Marine Corps recruits. Ten percent of the recruits whose blood tested positive for COVID-19 antibodies before training were re-infected with COVID while in basic training at Marine Corps Recruit Depot Parris Island, South Carolina. The findings make a strong argument for healthy young Americans to get vaccinated, according to researchers.