If vaccines other than AstraZeneca’s are available for young people, South Korean health authorities may want to consider an alternative, said Dr. Jean-Louis Excler, a vaccinologist at the International Vaccine Institute, as more countries limit the use of the vaccine to older people over blood clot concerns.

Excler, who is also part of the vaccine safety working group within COVAX, a global body that promotes equitable access to COVID-19 vaccines, said in an interview with The Korea Herald that the AstraZeneca question concerning young women, and some young men, was “real.”

“AstraZeneca’s might not be the preferable vaccine for young people -- if you have the luxury of a choice,” he said. “Given that extensive scientific knowledge on the matter is lacking, the worries of the rare blood clots in young people are legitimate.”

Though the European Medicines Agency maintains that the benefits of the vaccine continue to outweigh the risks for people who receive it, for young people the benefits versus risks are more complicated to evaluate, he said.

“The bottom line is that we don’t understand why. It is a question that nobody can give answers to. That’s why the regulators say further studies are needed.”

He said the recent decision of the Korean authorities to halt the AstraZeneca rollout for people under 60 years of age was “understandable” and “expected.”

The authorities here imposed the restrictions after two AstraZeneca vaccine recipients in their 20s reported experiencing serious blood clots. Neither had existing medical conditions. As 134,000 people under 30 have been given the vaccine so far in the country, this translates to a reporting rate of 1 in every 67,000 people.

But he was cautious to stress that in taking such precautions, each country must take into account vaccine availability and the pandemic situation.

Korea, for instance, has other options under its belt. Pfizer, Moderna, Novavax and Johnson & Johnson supplies sufficient to cover some 30 million people are coming in the next few months, according to the government announcement.

The pandemic situation here is also not that dire, relatively speaking, which may allow the country to wait for other vaccines to arrive until a better understanding is gained, he said.

“The important considerations are if there are enough of alternatives to circumvent this very rare risk, and if these alternatives are also free of any such risk,” he said.

“It must be noted that some thrombotic events have been described with other COVID-19 vaccines including those from Pfizer and Moderna and also with placebo recipients. But for the other vacines, such cases remain very sporadic and do not constitute a ‘signal’ as it is the case for the AstraZeneca vaccine.”

He said discussions among expert groups have yet to come up with an explanation for the mechanisms behind blood clotting following an AstraZeneca vaccination.

“What we are trying to figure out is the role of the vector and other components in the vaccine and natural factors that could be associated with the events,” he said.

“At our Brighton Collaboration meetings last week, we brainstormed at length about the possible reasons for these thrombotic events without coming to a common understanding. Unconvincing opinions were swaying between coincidence, the role of the adenovirus vector, the role of antigen, and background morbidity. No conclusion whatsoever can be drawn so far.”

He said while the AstraZeneca vaccine is the first vaccine employing a chimpanzee adenovirus to be approved for general use, chimpanzee adenoviruses have been tested in humans for vaccines against other infectious diseases, including Ebola, malaria, HIV and Crohn’s disease.

There is not enough information to warrant similar concerns with other adenovirus vector vaccines, Johnson & Johnson’s and Russia’s Sputnik V -- at least not yet.

“The cases seen in Johnson & Johnson are sporadic compared to the AstraZeneca situation. To the best of our knowledge, whether Sputnik V has triggered such events is not known to the public,” he said. “A meta-analysis of all trials is underway for the Ad26 (Adenovirus 26) vector.”

Asked to give advice for young women getting the AstraZeneca vaccine, especially young women on birth control pills or with a history of blood disorders such as thrombocytopenia, or a low platelet count, he said, “I’m sorry to repeat there is not sufficient data yet to recommend either for or against vaccinations in this group.”

Still, he said, some caution was probably justified. “It’s a fact at the moment that most of the cases have been observed in young women. I would say that it’s better to not include them in AstraZeneca vaccinations until more data becomes available.”

He said one of the issues now being discussed was whether those who have received one dose of the AstraZeneca vaccine should receive a second dose. “There are many studies being undertaken to see if we can mix and match the vaccines. It’s one of the scenarios that we are working on,” he said.

He said the drama surrounding the vaccine seemed driven not by real caution, but rather by political pressure. “There is a fear factor, also liability and political risks for those who recommend the vaccine’s use when so many remains unknown,” he said, adding that “we need to see the bigger picture here.”

“For any vaccine, it’s about weighing the benefits and the risks. The AstraZeneca vaccine is accessible, widely used in different countries. The risk of thrombotic events, so far rare, must be balanced against lives saved and hospitalizations avoided.”

By Kim Arin (arin@heraldcorp.com)