South Korea on Wednesday confirmed another case of a rare blood clot linked to AstraZeneca’s COVID-19 vaccine in a man in his early 30s.

The man was diagnosed with blood clots in his brain 12 days after his first dose of the vaccine, the Korea Disease Control and Prevention Agency told reporters in a closed-door briefing.

After receiving the shot on May 27, the man soon developed severe headache and nausea that worsened over time, the agency said. Nine days later, on June 5, he went to see a doctor but his symptoms persisted. He was hospitalized on June 8 with “decreased level of consciousness.”

The agency said his brain scans showed blood clots and bleeding, and that his platelet levels, too, had fallen. His tests for the PF4 antibodies, which are used to diagnose the vaccine-linked blood clotting condition, came back positive on Tuesday.

The agency said the man was in a serious condition at the hospital’s intensive care unit.

Since the man was not yet eligible for vaccination by age or occupation under Korea’s inoculation program, he got his shot through the leftover vaccine appointment system, the agency said.

This is the second reported instance of the rare, severe type of blood clot in an AstraZeneca vaccine recipient in Korea. The first case, announced on May 31, also involved a man in his early 30s who was diagnosed with clots in the brain 15 days after his first shot.

In response to a media inquiry asking if the benefits of AstraZeneca vaccinations still outweighed the risks in people in their 30s, the agency said “a review may be in order.” The cost-benefit analysis “may need to be redone based on recent statistics,” it said. Currently, people under 30 are offered an alternative to the AstraZeneca vaccine in Korea over a risk of rare blood clots.

As of Sunday, Korea has delivered AstraZeneca vaccinations to about 458,000 people in their 30s. Since this particular type of blood clot has been reported at a rate of 1 to 2 cases per 100,000 doses administered in Europe, the reporting rate here “does not appear to be high,” the agency said.

According to the agency, some of the symptoms indicative of the rare side effect include persistent or severe headache, blurred vision, shortness of breath, abdominal or chest pain, swelling in the leg and easy bruising. These symptoms tend to appear four to 30 days after vaccination.

This unusual blood-clotting condition is also associated with another adenovirus-based COVID-19 vaccine developed by Johnson & Johnson.

By Kim Arin (arin@heraldcorp.com)