Is there a link between the AstraZeneca vaccine and some cases of rare thrombosis?
The European Medicines Agency (EMA), in a report on the subject released yesterday, spoke of a “possible link” between the cases of “unusual blood clots with low platelets” reported after vaccination with AstraZeneca and the drug of the Anglo-Swedish company. ‘Adverse events’ have been described as a ‘very rare’ side effect which should be mentioned in the package insert and which healthcare professionals and recipients should be informed about. The WHO has called the link “plausible, but not confirmed”.
What is the incidence of thrombosis in the population?
The EMA spoke of one case for every 100,000 people, specifying that the number “varies greatly depending on the quality of the reporting system of the Member States and the quality of the cases identified”. Furthermore, at the beginning of the vaccination campaigns, in some countries it was chosen to vaccinate only certain categories with AstraZeneca and this variable may have altered the incidence ratio. As of April 4, the European Drug Safety Database had received a total of 222 reports on 34 million vaccinated people.
What is the benefit-risk ratio at this point?
The Ema has confirmed a positive relationship between risks and benefits in favor of the AstraZeneca vaccine, also because the Covid-19 disease in itself greatly increases the possibility of thrombosis.
Are there age groups most at risk?
It was said that the cases were recorded mainly among young adult women (under 55-60 years), but Ema stressed yesterday that “age, sex or previous medical history of bleeding disorders are not risk factors. , since rare events are observed in all ages and in men and women “, even if the Agency has reserved, in the future, to specify other indications.
Have governments decided on any restrictions on use?
Some European countries in recent weeks had already chosen to reserve the Oxford vaccine only for elderly people (generally over 60 years), precisely because of the slight increase in thrombotic episodes not seen in the older population. Other states decided to recommend the same preferential use last night, including Italy. It is a decision based on the calculation of Covid lethality and on how much this risk can balance the rare risk of thrombosis.
What did the UK decide and why?
In Great Britain it was decided to exclude AstraZeneca from vaccination for under 30s. This is based on some calculations that quantify on the one hand the possibility of hospitalization in intensive care by age group, on the other hand the frequency of serious adverse effects deriving from a vaccine. According to this scenario, the report is against immunization only in the 20-29 age group, which has a very low chance of hospitalization from Covid. Of the 79 people with reports of unusual blood clots in the UK, 19 died and three were under the age of 30.
Are there any categories that should be more careful, for example women?
There are no elements to say this, if not a purely numerical datum that depends on the type of population vaccinated. Pregnancy or oral contraceptives are also not currently considered discriminating risk factors.
Can another vaccine be used for the second dose?
From an immunological point of view it makes sense, because the second dose induces a strong immune response, however, specific clinical studies that have not yet been done would be needed.
What is the mechanism that triggers the adverse reaction?
The Ema confirms a possible explanation of the rare thrombosis with an autoimmune mechanism: after the administration of the vaccine, in some people the generation of so-called auto-antibodies is also stimulated, which “turn” towards the cells of our organism, in this case platelets and clotting factors.
April 8, 2021 (change April 8, 2021 | 06:55)
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