What are warning signs for rare blood clot syndrome after receiving COVID-19 vaccination?

Na Sang-hoon, a professor of circulatory internal medicine at Seoul National University Hospital, says you shouldn't be too concerned if you notice a bruise that gradually weakens and takes on a greenish tinge

A health worker prepares a dose of the AstraZeneca COVID-19 vaccine on April 26 at the Seoul Red Cross Hospital. (Yonhap News)

A 69-year-old Seoul resident received her first dose of the AstraZeneca (AZ) vaccine against COVID-19 on Thursday. Three days later, she saw a large bruise on the opposite arm from where she had received her shot.

The 69-year-old felt alarmed. She was aware that bruising in parts of the body other than the inoculation site is one of the symptoms of the side effect known as thrombosis with thrombotic syndrome (TTS), and she had also suffered a stroke in the past.

As it happened, she discovered the bruise on a Saturday. This meant that even if she underwent platelet level testing at a neighborhood hospital, she would not know the results for another three days or so.

She ended up visiting the emergency room at a large hospital. Blood tests showed that her platelet levels were normal.

South Korea recorded its first death attributed to rare blood clots associated with a COVID-19 vaccine on Wednesday. Confusion and fear are growing among others who have received the jab as they wrestle with how to respond to this rare but potentially deadly side effect.

On Monday, the South Korean government announced that a meeting of the vaccination harm investigation task force had been held on Friday after the death of a man in his early 30s who had been diagnosed with TTS.

A causal relationship between the vaccine and the condition was officially recognized during the meeting, the government said. The side effect is one that can occur in people who have been administered an adenovirus vector vaccine, such as those made by AZ or Janssen.

“My mother didn’t have a headache or any other symptoms besides the bruise, and she was at a loss over whether she needed to go to the hospital or not,” the 69-year-old’s daughter said — who accompanied her mother on her hospital visit due to the bruise — in a telephone interview with the Hankyoreh on Monday.

“On the day we went, the emergency room doctor at the major hospital said they’d already been visited by five people that day who had developed bruises after their shots and that all of them were found to have normal platelet levels,” she added.

On June 10, a 62-year-old Gyeonggi Province resident discovered bruises on their knee and the opposite arm from where they had received their shot five days earlier. But the bruise gradually faded, and since they were not experiencing any other symptoms, the 62-year-old decided to wait rather than going to a hospital.

“They said [TTS] is a side effect that mainly occurs in younger people, and I felt like it would be making a mountain out of a molehill, but I was also nervous,” they said.

“I’d like to see the government being explicit about what extent the bruising should be for you to have to go to the hospital.”

Many have also posted online about undergoing complete blood count testing to check their platelet levels after experiencing bruising after their vaccination.

On Monday, the COVID-19 vaccination response task force provided another explanation of the symptoms associated with TTS, advising that those who experience them “should immediately receive treatment at a healthcare institution, and that healthcare institution should immediately report the adverse reaction.”

The symptoms included severe headaches that do not respond to painkillers, headaches that last for two days or longer, vomiting, blurred vision, difficulty breathing, sustained abdominal pain, swelling in the arms and legs, and bruising or bleeding in areas other than the vaccination site.

With regard to bruising, Park Young-joon, director of the task force’s adverse reaction investigation team, said, “If you discover bruising in places other than the vaccination site following smaller impacts than usual, you should suspect that and visit a healthcare institution.”

“The time frame should also be taken into account,” he added, referring to the fact that symptoms typically appear between four and 28 days after vaccination.

Na Sang-hoon, a professor of circulatory internal medicine at Seoul National University Hospital, said, “Thrombosis with thrombocytopenia syndrome is a condition that gets worse without treatment, so if you notice a bruise on your body gradually weakening and taking on a greenish tinge, you shouldn’t be too concerned.”

“The side effect is something that occurs with the breakdown of platelets that last for three to four days, so you also don’t need to be very worried about bruising that occurs less than four days after vaccination,” he added.

But Na also said, “If bruising occurs not on protruding parts of the body like your elbow but on parts where it typically does not occur, such as behind your knee or on your torso, or if you’re experiencing viscous bleeding across your body, you should immediately go to a healthcare institution for testing.”

By Choi Ha-yan, staff reporter

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