Covid-19 increases the risk of cerebral thrombosis (and probably much more than after a vaccine)

Covid-19 increases the risk of cerebral thrombosis (and probably much more than after a vaccine)

A preprint study analyzed the incidence of cerebral venous sinus thrombosis among Covid patients, establishing that it is much higher than that found in the general population, and probably also vaccine-related ones

( photo: David Ramos / Getty Images) While EMA's decisions on the Johnson & Johnson-Janssen vaccine (whose distribution in Europe is currently stopped by decision of the same company) are awaited, and countries such as Denmark have completely suspended the administrations than AstraZeneca, the research works hard to clarify the real risks posed by the two adenovirus vaccines against Covid-19. Not an easy undertaking, because we are talking about extremely rare potential adverse events not only in the vaccinated population, but also in the general one. Which must be carefully weighed even against those posed by the disease: it is known that cerebral venous sinus thrombosis is one of the possible complications related to Covid 19. How often? New British research has tried to establish this once and for all, analyzing the incidence of the problem in over 500,000 American patients with Covid, to determine whether the risks posed by the disease exceed, or not, those potentially related to the vaccine. And even with many limitations, the response would seem reassuring: cerebral thrombosis would in fact be more common with Covid-19 than it is with vaccination.

The limits, we said, are however different: the study is currently available in preprint on the Open Science Framework platform, and therefore does not have the degree of certainty of a study that has passed the peer review process. Furthermore, it is not a study that directly compared the incidence of cerebral venous sinus thrombosis between Covid patients and people vaccinated with adenovirus vaccines, and can therefore only tell us what the incidence of the problem is following the disease, but not which one receives the AstraZeneca or Johnson & Johnson vaccines. To attempt a comparison, the researchers used the numbers provided by the Ema analysis on the AstraZeneca vaccine on April 7, obtaining an incidence data by comparing the number of adverse events reported with the total number of vaccinations performed up to that moment. But it is clear that, since these are very different samples, the comparison between the two numbers must be taken with a grain of salt.

Having removed the limits of the research, it is obviously necessary to also talk about its merits: it is a matter of of a study with a large sample of participants, and with three control groups represented by a second group of patients affected by influenza, and almost 500 thousand other people who were injected with one of the two mRna vaccines, Pfizer or Moderna . What do the results say? That in the population analyzed the risk of developing cerebral venous sinus thrombosis is much, much higher following Covid 19 than all the other events analyzed. In Covid patients, the incidence is in fact equal to 39 cases per million, in people vaccinated with Pfizer or Moderna we drop to just 4 cases per million, and in patients with the flu we even reach 0 cases per million.

Taking the estimate of the incidence of cerebral thrombosis in people vaccinated with AstraZeneca calculated on Ema data, equal to 5 cases per million, also the risk / benefit ratio of the vaccine becomes absolutely positive: getting sick with Covid-19 the risk is almost eight times higher than what you run by getting vaccinated. Of the cases that emerged in the study following Covid-19, 14 out of 20 were recorded in people under 60, which would bring the incidence of cerebral venous sinus thrombosis before the age of 60 to about 28 cases per million, however higher than that emerged for the general population and for the vaccinated. And even for those under 30, the cases are about 12 per million. A large number, but which becomes extremely difficult to compare with the other categories because the samples are not uniform in terms of age and other demographic factors.

So, how should we interpret the results of the study? They certainly give us a more precise idea of ​​the risks of developing cerebral venous thrombosis that a Covid patient runs, and they tell us that, although low in absolute terms, they are quite high, being an extremely rare problem even in the general population. Speaking of adenovirus vaccines, it is not possible to make a direct comparison, but the high incidence of the problem following the disease certainly helps to put the dangers in perspective, and to reduce them. Also because it must be remembered that getting sick with Covid-19 does not only expose you to the danger of thrombosis, but to a wide range of potentially fatal complications. It is therefore a very difficult assessment, which should also take into account the personal risks of contracting the virus. As it is easy to see in this series of slides created by the University of Cambridge, the relevance of the potential side effects of vaccines decreases as the chances of contracting the virus increase:

Risk / Benefit Profile of the AstraZeneca vaccine in one low virus circulation scenario (image: University of Cambridge) AstraZeneca vaccine risk / benefit profile in a medium virus circulation scenario (image: University of Cambridge) AstraZeneca vaccine risk / benefit profile in a high circulation scenario virus (image: University of Cambridge) To pull the strings, in short, it is too early to say what are the individual dangers associated with vaccination with AstraZeneca or Johnson & Johnson - Janssen vials. What is certain is that if they exist they are really very low, and are counterbalanced (in a more or less large proportion) by those that occur in case of illness.

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Coronavirus Thrombosis vaccine AstraZeneca-Oxford Coronavirus vaccine Johnson & Johnson vaccine globalData.fldTopic = "Coronavirus, Thrombosis, AstraZeneca-Oxford vaccine, Coronavirus vaccine, Johnson & Johnson vaccine"

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