Hard choices emerge as link between AstraZeneca vaccine and rare clotting disorder becomes clearer - Science Magazine

What was a worrisome suspicion four weeks ago is now widely accepted: The AstraZeneca COVID-19 vaccine can, in very rare cases, cause a disorder characterized by dangerous blood clots and low platelet counts.

In Europe, at least 222 suspected cases have been reported among 34 million who have received their first dose of the vaccine.

The researchers who studied the German and Austrian patients, led by clotting expert Andreas Greinacher of the University of Greifswald, had initially called the syndrome vaccine-induced prothrombotic immune thrombocytopenia, or VIPIT; both teams now suggest a slightly simpler name, vaccine-induced immune thrombotic thrombocytopenia (VITT).

Among the 50 billion or so virus particles in each dose, some may break apart and release their DNA, Greinacher says.

Alternatively, the antibodies may already be present in the patients and the vaccine may just boost them.

Many healthy people harbor such antibodies against PF4, but they are kept in check by an immune mechanism called peripheral tolerance, says Gowthami Arepally, a hematologist at Duke University School of Medicine who is working as an external consultant with AstraZeneca on the issue.

Among more than 200 patients who had recovered from COVID-19, they found only a few with antibodies that reacted to PF4, and those reacted relatively weakly.

More importantly, Greinacher says, the platelet-activating antibodies isolated from VITT patients did not react to the coronavirus spike protein.

patients who had received the Johnson & Johnson vaccine, which has been used in the United States since early March but has yet to make its debut in Europe.

The cases could be coincidence, Greinacher says, but “it’s at least very suspicious.”.

Nevertheless, many countries have restricted its use in younger people.

They reason that younger people are at lower risk of getting severely ill and dying from COVID-19, making it harder to justify the risk of side effects.

In the United Kingdom, a vaccine advisory panel has recommended that people younger than 30 be offered a different vaccine.

Based on currently available data, the risk of serious harm due to the vaccine for people aged 20 to 29 in the United Kingdom is about 1.1 in 100,000, says David Spiegelhalter, a statistician at the University of Cambridge.

Getting vaccinated also provides protection to other people, Spiegelhalter says: “I think that's an aspect that has not been emphasized enough.”.

(The country has recommended people under 50 receive a different vaccine when possible.) The availability of alternatives is an important consideration as well.

In AstraZeneca's phase III trial in the United Kingdom, a small number of people accidentally received a lower dose and had fewer side effects in general; perhaps the lower dose is less likely to trigger the kind of strong inflammation that boosts PF4 antibodies as well, the researchers say.

And unexpectedly, those people were slightly better protected, perhaps because high levels of inflammation can actually block the formation of antibodies, Marschalek says.

“Part of the problem might be that they just overdose” the vaccine, Greinacher says.