Rare vaccination side effects: should we care?

Many people worldwide are currently worried about possible side effects of the new AstraZeneca vaccination. Media reports focused at first on thromboembolic events, then on sinus vein thromboses, subsequently leading half of Europe to interrupt their vaccination programmes. This did not foster trust.

However, let’s try to assess the possible risks more objectively. EMA received reports of 18 sinus vein thromboses after around 20 million AstraZeneca vaccinations by 16 March. From a scientific perspective, it’s still not clear, if or how many of these events were caused by the vaccine. Nevertheless, for the sake of illustration, let’s assume that all of them were caused by the vaccine and even that all of them might have been deadly (which was not the case). This would mean that one million vaccines may lead to one death. Would this be reason enough to not get vaccinated?

Side effects of fewer than one in 10,000 are defined as ‘very rare’ by package inserts. The side effect of our example, one in a million, would therefore be 100-times less common than ‘very rare’. Would that be justified? It arguably would. According to UK mortality data, a 30-year-old man has on average the risk of one in a million to die within the next eleven hours. A 60-year-old woman has the same mortality risk even for the upcoming two hours. Life inherently carries risks. Even getting to the vaccination site is not without risks — if you drive eight miles by motorcycle, your risk of death is one in a million. Your risk of being struck by lightning in one year is already twice as high (based on CDC data). The risk of death of one in a million is so small, that we accept it several times a day without giving it a thought.

Based on current knowledge, the AstraZeneca vaccine not only has an (extremely low) risk, but also an advantage, namely avoiding harm by a SARS-CoV-2 infection. Being infected puts us at an average risk of around one in one hundred to die. Many people who now worry about developing a thromboembolic event may not know that more than one in ten patients hospitalised with COVID-19 are being diagnosed with it, several thousand times more frequently than recently reported thromboembolic events after the AstraZeneca vaccination.

Ultimately, the decision in favour or against getting vaccinated is a personal decision. Many factual arguments are supportive but concerns and worries may stay after the recent media reports. However, we should probably be more afraid of being struck by lightning than of receiving a sinus vein thrombosis due to the AstraZeneca vaccine.

I declare no conflicts of interest.

A different version of this article was published in German in DerStandard.