An Army soldier in his 20s has died six days after receiving his first dose of Pfizer's coronavirus vaccine, officials said Monday.

The soldier, based in Seoul, was found unconscious in his barracks the previous day and transferred to a nearby hospital but died.

It wasn't immediately clear if the death was directly related to the vaccine.

An autopsy is planned to look into the exact cause of the death, officials said.

It is the second death of a service member following COVID-19 vaccination.

Earlier this month, an Air Force noncommissioned officer in his 40s died after receiving a second dose of the AstraZeneca vaccine.

It was not determined if the vaccine was connected to the death as the surviving family didn't want an autopsy done on the late officer.

The military began administering Pfizer's COVID-19 vaccine to soldiers under 30 last week. As of Friday, 162,053 service members, or 40 percent of troops under the age group have received their first doses.

Soldiers aged 30 and older were given AstraZeneca's vaccine, with about 88 percent, or 116,900 members agreeing to take their first shots.

On Monday, the ministry said two Army officers based in Pocheon, 46 kilometers north of Seoul, have tested positive for the new coronavirus, raising the total number of infections reported among the military population to 995.

Nationwide, South Korea added 399 new cases, bringing the total caseload to 148,273. It marked the first time in more than two months for the daily figure to fall to the 300s since late March. (Yonhap)