What we know about the higher prevalence of thrombi in young women vaccinated with AstraZeneca and Janssen

If the preliminary data seem to point, very slightly, to a higher prevalence of thrombi in women in general, and young women in particular, who have received the AstraZeneca vaccine, should we advise against getting this group of people vaccinated? Is it the same with other medications? Are women simply more prone to thrombi?

We are going to try to answer all these questions, while contextualizing the risks we face.

Thrombus prevalence in women? Not so fast

According to data, cerebral venous thrombosis has an incidence of 1.3 cases per 100,000 people per year. But in the case of women, the figure rises to 2.7 cases. 60% of cases of this type of thrombosis occur in young women under 45 years of age, probably due to hormonal factors, among others.

Among the risk factors for producing a thrombosis are also oral contraceptives, pregnancy and the use of hormonal therapies, among others.

Women they also suffer from more autoimmune diseases And the younger they are, the more active their immune systems are. That is, they can react intensely to vaccines, and as a new study by medical teams from Austria and Germany suggests. As the study describes, in all cases in which a thrombus has occurred with patients who received AstraZeneca it appears that there was a reaction in which the immune system turned against the patient itself.

Among the risk factors for producing a thrombosis are also oral contraceptives, pregnancy and the use of hormonal therapies, among others.

Now let’s go to the cases that have been linked to the AstraZeneca vaccine. Most of these events occurred within 14 days of vaccination, in people under 55 years of age and, mostly, in women.

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Are we facing a problem? With the data we have, it doesn’t seem like it. Therefore, the European Pharmacovigilance Committee (PRAC) has not concluded that age and gender were clear risk factors for these rare side effects:

Sabine Straus, President of the PRAC: “Although the majority of the cases occurred in people under 60 years of age and in women, due to the different ways the vaccine is used in different countries, the #PRAC did not conclude that age and sex were clear risk factors for these rare side effects. “

But doesn’t AstraZeneca seem to raise the number of thrombi in women? The truth is, we can’t make a statement like that so lightly. In fact, it would be scientifically irresponsible. claiming that there is such a concrete causal link for various reasons.

Just because someone gets a thrombus after getting the vaccine does not mean they got it from getting the vaccine.

First of all, because there are very few cases among millions of people who have already been vaccinated. Just because someone gets a thrombus after getting the vaccine does not mean they got it from getting the vaccine.

The vaccine has been administered to more than 20 million individuals, making it easier for perhaps we can detect rare diseases that would have gone unnoticed without the intense medical and social surveillance of vaccinated people. Furthermore, in vaccinated patients it has been observed that the risk of venous thrombosis it is even lower than that of the general population, a fact confirmed by the EMA in its last communication.

Second, we do not know if the characteristics of the vaccinated populations (different between countries) may be skewing in some way the results we are trying to analyze. Furthermore, the procedure by which cases of thrombi and low platelet levels are recorded is not homogeneous between EU countries.

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As if all this were not enough, even today the mechanism by which thrombi would occur continues to be unclear, although the hypothesis that has more solidity is, for the moment, that it is due to an effect of the autoimmune response.

We will insist on it: It cannot be said that the AstraZeneca vaccine increases the risk of thrombosis in any group of patients, not even in young women. We are only facing hypotheses. Its association with the AstraZeneca vaccine has not been demonstrated at the moment, and the cases observed have been very scarce, close to the expected incidence in the general population already mentioned.

If the pharmacovigilance alarm has been activated, it has been as a security measure, as a preventive measure. The data are not enough to stop recommending the vaccine.

Regulatory Bodies Actions

Although the EMA does not have sufficient evidence to conclude the cause of thrombi, it suspects that it may be due to the production of antibodies that attack a protein involved in clotting; a study supports this cause, which has a treatment.

But the EMA, he insists, you do not know if these thrombi really affect women under 60 years of age more. It cannot be ruled out that this group is at risk, but perhaps we are facing some kind of statistical distortion. It is also not known what exact component of the vaccine would generate this autoimmune reaction. Over the next few months, it is expected that both the EMA and various groups of researchers will clarify these issues. You have to be patient.

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Refering to Janssen vaccine, distribution has been delayed in Europe after the recommendation of the health authorities to paralyze it in the United States, where they have found six cases of thrombi among seven million vaccinated. Janssen has thus delayed delivery dose in the EU. As confirmed by the EMA, and following meetings with the PRAC safety committee, a case review has thus been initiated to investigate these unusual events in people vaccinated with Janssen.

A pause that affects the vaccination of hundreds of thousands of people who could die or become ill from COVID.

But again we are having the same problem as with AstraZeneca. There are very few cases. These measures are taken to take extreme precautions.

However, the logistics and price facilities have made the Janssen vaccine the one that has raised the most hope when it comes to fighting Covid-19. A pause that affects the vaccination of hundreds of thousands of people who could die or become ill from COVID. Especially if we speak in developing countries.

In such a case, perhaps the agencies are exceeding their precautions. The social, media and even political component, then, probably also has a lot to do with the application of such strict measures, as we will see below.

General and specific risks: context

Let’s start with the general risks of thrombosis to contextualize the data we are analyzing. Thrombosis is a low frequency phenomenon, which affects more certain profiles of individuals. It is estimated that, globally, can occur in 1-2 out of every 1,000 individuals in each annual period.

How the EMA has calculated that the benefits of vaccinating with Astrazaneca far outweigh the risks by age group

As for patients with COVID-19, the risks, and this is very important, increase a lot. Namely, just by being infected, the risk of thrombus is higher (If you are vaccinated, the risk of getting it falls, naturally). The risk of thrombosis is highly variable, but in critically ill patients (in ICU) it is estimated that thrombi reach 20-25% of cases. In non-critical hospitalized patients this risk is lower, 5%. Patients with mild disease, who do not require admission, the risk is estimated at 1%. In all cases, it is always superior to that of the vaccine.

We can therefore say that in general that the risk of suffering a clot is 19,500 times higher from getting COVID-19 than from AstraZeneca vaccination.

In our country, only 0.18% of those vaccinated with AstraZeneca have had adverse effects, but especially fever, headache and muscle pain. On the other hand, the rate of women suffering from blood clots when using contraceptives is much higher: in fact, the risk of a clotting disorder is 167 times higher, on average.

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Does it mean that contraceptives are dangerous? Not, what it means is that all drugs have adverse effects, and they continue to be used because the benefits outweigh the risks. For example, naproxen, an anti-inflammatory drug used to treat mild to moderate pain, can cause gastrointestinal bleeding in one case in a thousand.

And beyond medications, there are many daily activities that also have risks, even risks associated with thrombi. According to the NICE institute (the UK’s National Institute for Health and Care Quality), the risk of suffering from a thrombus is 250 times higher when taking a flight than when getting vaccinated with AstraZeneca.

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Then? Why is there such a stir with the adverse effects of vaccines? Why are regulatory bodies taking so many actions? Basically it all comes down to a single question: eWe are facing the first global pandemic 2.0.

If we read the Pharmacovigilance report:

Adverse event reporting is not a tool that can be used to estimate the frequency of occurrence of adverse reactions in vaccinated people, as it is not a systematic collection of data and as mentioned above, these are not necessarily events related to vaccination. Nor is it useful, therefore, to make comparisons on the safety of different vaccines.

What’s more, adverse effects reported in the real world are much lower than those documented in clinical trials (where they are collected systematically). The purpose of this report, therefore, is not to record correct frequencies of all adverse effects. that have already been documented, but rather detect those serious or unexpected adverse effects that have not been previously detected in clinical trials.

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Many measures are not taken, therefore, they are taken with this in mind. Of course, one wonders if vaccination with AstraZeneca or Janssen would have been stopped if the results of the pharmacovigilance were not broadcast in real time, nor had so much media visibility. Probably not. For this reason, there is the paradox that nobody or almost nobody observes problems in the fact of using experimental treatments for COVID-10, such as hydroxychloroquine or azithromycin, which have later been found to be useless, but many feel like guinea pigs in the face of vaccines.

In the end, we care about what we magnify. And medicine, even if it is not comfortable for us, always carries a percentage of uncertainty that is difficult to eliminate. Faced with new treatments, pharmacovigilance tries to minimize this uncertainty. But it will always exist, as Bertolt Brecht said in Galileo’s life:

The goal of science is not to open the door to infinite knowledge, but to set a limit to infinite error.


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