Investigations are underway after two South Korean recipients of the AstraZeneca vaccine died following inoculation against the coronavirus disease 2019 (Covid-19).

Both recipients had been in long-term care, officials said.

South Korean health authorities said Wednesday that the two patients, both men, showed symptoms of rapidly declining health after being given the AstraZeneca doses, Yonhap and YTN reported.

A 63-year-old recipient in Pyeongtaek, Gyeonggi province, was reportedly given the vaccine on Saturday afternoon while hospitalized for cerebrovascular disease. On Sunday, he developed a fever and body aches.

A doctor at the hospital prescribed pain relievers, but after a brief recovery, the man’s symptoms worsened on Tuesday. He died on Wednesday morning, according to Yonhap.

The second recipient, identified as a man in his 50s, received the vaccine while hospitalized at a clinic in Goyang city in the same province, YTN reported.

The man was given the inoculation Tuesday. He experienced breathing difficulties and died after multiple heart attacks, according to the report.

Another man undergoing care at a hospital in the city of Uijeongbu showed signs of immobility and headaches after being administered the vaccine. His condition had stabilized by Wednesday, according to YTN.

AstraZeneca’s vaccine rolled out in South Korea on Feb. 26, but doses are off-limits to people age 65 or older.

South Korea’s military is using supplies from the British-Swedish firm and the United States’ Pfizer to vaccinate troops.

News 1 reported Wednesday that COVID-19 vaccinations had begun at 16 military hospitals, with the first doses to go to doctors, nurses and frontline health workers for a total of 2,400 people.

South Korean soldiers are to receive the vaccines by the end of the second quarter, and “according to priority,” Seoul’s defense ministry said.

South Korea has reported more than 90,000 cases of COVID-19 since the start of the pandemic. On Wednesday, the country added 444 new cases and six new deaths.