AstraZeneca’s COVID-19 vaccine will not be given to anyone under the age of 30 in South Korea, as growing evidence points to possible associations with a rare but serious blood-clotting disorder.

The government’s advisory committee on immunization practices said in a news briefing Sunday that AstraZeneca vaccinations will resume Monday after a partial suspension for the last four days.

In an emergency announcement Wednesday evening, the immunization advisory committee said it would be temporarily limiting the AstraZeneca vaccine’s use to people older than 60 years following reports of a second recipient in their 20s having developed blood clots.

The committee convened a meeting Saturday and concluded that for people aged 29 or younger, who were originally eligible for AstraZeneca shots, will be offered an alternative as a precaution.

However, it stands by its earlier stance that the benefits of AstraZeneca vaccinations still outweighed the risks of side effects for the other age groups. Blood clots, induced by the vaccine or otherwise, were treatable and nonfatal if detected early, it explained.

To encourage early diagnosis, the official advice on the AstraZeneca vaccine for the public will now include a rare blood clot risk accordingly, and when to seek medical attention in the event of suspected signs and symptoms, the committee said. Previously, the warning was only listed in the vaccine product information, updated after the European Medicines Agency report last month that suggested caution.

The committee said that as infection rates once again rise in the country, continuing vaccinations is paramount in containing the pandemic and reducing deaths and hospitalizations.

While excluding people under 30 from AstraZeneca vaccinations from this point on, the committee added that people who have already had one AstraZeneca dose will still get a second one regardless of their age. Giving them a second shot of a different vaccine is not being considered at the moment, it said.

“AstraZeneca’s is one of the two vaccines that Korea currently has access to, and indubitably a vital tool for pandemic control in the country,” said Jeong Eun-kyeong, who is overseeing the COVID-19 vaccination campaign in the country as the Korea Disease Control and Prevention Agency Commissioner.

She said the call to carry on with vaccinations was based on the benefits-to-risks evaluation and the latest information from Europe, and once again urged the public to get the vaccine at their turn.

The EMA’s Friday statement recognized a “possible link” between the AstraZeneca vaccine and rare blood clots. The agency also said it started reviewing incidence of another blood disorder called capillary leak syndrome in people who took the AstraZeneca vaccine, adding that the emerging reports constituted “a safety signal.”

So far out of around 140,000 people aged between 18 and 29 who received at least a single dose of the AstraZeneca vaccine, two reported having developed blood clots within two weeks of the inoculations.

One of them was a first responder who was diagnosed in mid-March with an unusual type of blood clotting in the brain called cerebral venous sinus thrombosis. The other was a medical worker who came down with a pulmonary embolism earlier this month. Neither had preexisting health problems.

The former was given immunoassay for the platelet-activating antibodies known to cause the serious clotting disorder and tested negative; the latter was not tested for the antibodies.

Researchers in Germany and Norway found that the blood clotting disorder observed in AstraZeneca vaccine recipients resembled an unusual side effect to blood thinner heparin called heparin-induced thrombocytopenia -- but without a preceding heparin exposure. They said the antibodies that activated platelets were found in the recipients, which led to the clots.

Jeong said the two clotting cases in 20-somethings did not seem congruous with the type of blood clots accompanied by low platelet counts outlined by the EMA, but admitted that one of them might be linked to the vaccination.

Following Sunday’s decision, the second phase of the mass vaccination campaign in Korea -- targeting residents of group homes and noncoronavirus essential workers such as early childhood educators -- will begin Monday.

By Kim Arin (arin@heraldcorp.com)