Let's try to better understand the risk of an adverse event after the Covid-19 vaccine

The perception of risk is often subjective and instinctive, but the numbers tell us that every day we expose ourselves to much higher risks than those of the rare adverse effects of vaccines against Covid-19. Here are some comparisons

(photo: Mohammad Shahhosseini / Unsplash) One of the most difficult issues to communicate, long before the start of the Covid-19 pandemic, is the exposure to risk and the actual danger to which we are exposed in an emergency situation. It could be said that reason and science require us to make it primarily a numerical question, of quantitative analysis and statistics, but it has been known for some time how much in reality the topic - especially when we move from evaluations between professionals to the general public - is permeated also by aspects related to subjective perception, emotionality and our innate instinctive reaction in front of a potential danger, which sometimes translates into apparently irrational actions dictated by cognitive distortions of various kinds.

A common feature of many evaluations that can be read online and in the newspapers about vaccination risk (and which are also heard in the collective chatter) is the attempt to compare the various vaccines. Not only in terms of general efficacy and against specific variants, but also in terms of the incidence of more or less significant adverse effects that may follow vaccination. So, for example, we focus on whether one or the other formulation has a slightly higher or a little lower frequency in the rare side symptoms that it can cause: an undoubtedly important issue to monitor at level of pharmacovigilance, and returned to the fore in the last few days after the umpteenth changes to the indications for use for the Vaxzevria vaccine from Oxford-AstraZeneca. But that could lead one to think that vaccine comparisons are crucial, when instead, even in the worst case scenario, the risk in question is extremely low.

An undoubtedly remarkable example of the comparative work is that offered by Reuters, while in other cases it was preferred to focus on the general comparison between Covid-19 risk vs vaccination risk (here the University of Cambridge, to give an idea) or on a comparison between the risk of thrombosis with and without vaccination. In absolute terms, however, to date both for the Anglo-Swedish vaccine and for the Johnson & Johnson vaccine (which at the moment has different indications for use, although it is not clear why), the incidence estimates of the rare thrombotic side effects they are one in every 100 thousand vaccinated, if not even less.

Does it make sense to make comparisons with other drugs?

A further possibility of comparison, again with regard to the risk of adverse effects, is to compare the anti Covid-19 vaccines with other commonly used drugs. The result is obvious, even without going into the details of the numbers: vaccines are by far among the safest drugs, both in general and in the specific case of those against Covid-19. And several of the most common painkillers, antipyretics and anti-inflammatories have an incidence of side effects - even serious ones - that are far higher than those of a vaccination.

On a communicative level, however, this argument often struggles to hold up, because the a typical objection of those who are hesitating to get vaccinated is that one thing is the drugs we take when we are sick (accepting more willingly to take a risk, but in exchange for a perceptible benefit) and another are those that have a preventive purpose , which we assume when the problem has not yet manifested itself. Not that the objection itself is conclusive - the vaccine reduces the risk of complications in those who become infected with the virus, and the risk of contagion is certainly not negligible, indeed unfortunately quite high, in the long term - but let's pretend welcome it.

One of the exceptions to this communication impasse are contraceptives for female use, which are certainly not usually drugs for patients and yet have already been shown to have a certain correlation with the thromboembolic events themselves: not one in 100 thousand like the anti Covid-19 vaccines, but between 3 and 9 per 10,000, or at least higher than 2 per 10,000 according to a mammoth study in the British Medical Journal of the last decade. This obviously does not mean that it is a bad idea to take a contraceptive (and God forbid), but that from the point of view of the most serious adverse effects the risk is at least ten times higher than that of vaccination.

More than the vaccine, the light bulb and the bath in the sea

In summary: it may not be enough to argue that the risk of getting vaccinated is much lower than that of the disease from which it protects; it may not be enough to show that the vaccine has a much lower level of risk than commonly used drugs; it may not be enough to compare the incidence of certain adverse effects with those that occur in any case in the general population; and it may not be enough to give the absolute numbers of these risks (specifying, for example, that only in one out of three cases the thrombosis caused by the vaccine translates into a fatal clinical outcome, and that if instead of thinking about the twenties we pass to the fifties the risk of thrombosis is further reduced to one third). But what about the risks that, as healthy people, we run daily in doing our routine activities, and what numbers in hand are much more problematic than undergoing vaccination?

Let's give some examples. Also referring to 100 thousand people, according to the Winton Center for Risk and Evidence Communication and an analysis by the BBC, the annual risk of dying from a car accident is estimated at 38 for young people and 23 for middle-aged people. (versus 11 and 4 in the case of the AstraZeneca vaccine). To die from any type of accident fluctuates between 110 and 180 each year, and only in the case of deaths from lightning do we have another 1 to add each year. The risk of not surviving the vaccination, in other words, is comparable to that of being the victim of a murder in the next 30 days, or to that of a 400-kilometer car ride.

Indeed, in in many cases, even when you are in the vaccination center for the injection you are safer than anywhere else, including the walls of your home. For example, statistics in hand, the risk of dying climbing a three-step home ladder for routine maintenance (like changing a light bulb) is 9 times that of vaccination if you are a woman, and 37 times that of vaccination if you are a woman, and 37 times that of vaccination if you are a man. taking into account the likelihood of accidental falls and the risk of being electrocuted by the electrical outlet. The probability of dying from the Covid vaccine is roughly half that of being killed by your partner in a Western country, and roughly half as much as that of drowning (from illness or otherwise) during every single swim in the sea. .

Every bike ride has a risk of fatal existence compared to a dose of anti-Covid virus with a virus that is 2.5 times higher, and the same is true on average for every day spent at the place of work . Comparing with other long-standing statistics, the risk of getting vaccinated corresponds to that of traveling 16,000 kilometers by plane, or 100,000 by train, a couple of hang-gliding trips, walking a total of 270 kilometers (not all at once) or to travel 95 kilometers by motorbike. Again, in indirect terms and for example through the diseases it can cause, a vaccine corresponds to the risk of smoking 14 cigarettes or drinking 5 liters of wine.

On balance, a person who leads a life of all average effects (no extreme sports, no excesses of alcohol, smoking, drugs or junk foods, no special work activities, extravagance or unnecessary gambling) has a risk of dying for every week that he simply lives - that is, he gets out of bed and undertakes your day - equal to twice the time you get vaccinated. The perception of risk will in any case remain subjective, but not getting vaccinated for fear of adverse effects rationally makes little sense if you intend to continue to lead a life that is not just lying on the mattress, and that includes, for example, moving, working, take some medication as needed, to live with your partner or to go on vacation.


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