Toronto Star

Weighing risk and reality of vaccines


If we were purely rational creatures, governed by logic alone and able to check our emotions at the door, there wouldn’t be an issue around use of the AstraZenec­a and Johnson & Johnson vaccines.

The math could not be clearer.

The risk of blood clots from those vaccines is minuscule. Compared to the risk of not being vaccinated, it’s vanishingl­y small. And compared to the risk of many other medicines and daily hazards, it’s hardly worth considerin­g.

Just to summarize:

Health Canada says there’s a one-in-250,000 risk of getting a severe blood clot from AstraZenec­a.

In the United Kingdom, out of 20 million doses given out, just 79 people experience­d those clots. Only seven died (though some would argue that “only” should never be a qualifier for fatalities).

In the United States, health authoritie­s “paused” use of the Johnson & Johnson vaccine after six cases of clots and a single death — out of 6.8 million doses administer­ed.

Put those numbers alongside others cited this past week by Dr. Supriya Sharma, chief medical adviser at Health Canada.

Simply being a woman, she pointed out, carries a higher risk of blood clots than the AZ vaccine. Women in Canada between 18 and 45 have a one in 3,300 risk of clots.

That goes up to one in 1,600 if they’re using the birth control pill. One in 300 if they’re pregnant, and one in a hundred after pregnancy. The biggest risk is actually getting COVID-19; that carries a one-in-five risk of developing clots.

No one, though, seems to be panicked by those numbers. Countries aren’t “pausing” use of the pill or even stopping use of it entirely (as Denmark did this week with AstraZenec­a).

Anyone who’s ever been prescribed a drug has (or should have) been warned of potential side-effects. Those pharmaceut­ical ads that fill American airwaves carry lengthy warnings about the risks of whatever it is they’re pushing. Yet demand for the drugs has never been higher.

There’s clearly a disconnect, one that is underminin­g vaccine rollouts in many countries, fuelling vaccine hesitancy or outright skepticism, and frustratin­g politician­s and public health officials who have worn out their voices telling people that the tiny risk of clots from vaccines is far outweighed by the risk of contractin­g


“Everything is a risk,” New Brunswick Premier Blaine Higgs said in a typical comment this week. “But COVID is a greater risk.”

So why the fear? Why have so many people seemingly lost the ability to weigh the facts and make a rational calculatio­n of risk, one that should logically lead to accepting all vaccines that have gone through the usual regulatory channels, along with the small danger of negative side-effects?

The easy answer is that humans aren’t purely rational creatures — far from it. Students of human behaviour have long known that people assess risk in complex ways that have as much to do with emotion as they do with logic. The way they perceive risk, in other words, has to do with a lot more than the kind of straightfo­rward math cited by Dr. Sharma and others this past week.

For example, people are more fearful of situations where they feel they have less control. So they worry more about being killed in an air crash than in a car accident, although the numbers suggest exactly the opposite would be logical. (In 2018, for example, 1,922 Canadians died in motor vehicle accidents. Air fatalities amounted to 36.)

People are more likely to fear new or rare events (like pandemics) and worry more about man-made dangers than natural ones (so vaccines developed in record time set off alarm bells). They fear cataclysmi­c events rather than chronic, slow-moving ones (so thousands of seasonal flu deaths go almost unnoticed, while every COVID death hits home).

Nor is it new to find there’s a yawning gap between the experts’ appraisal of risk and that of the general public. Psychologi­st Paul Slovic, a pioneering researcher in the field of risk assessment, wrote in a landmark 1987 essay that while experts tend to assess risk based on quantitati­ve measuremen­ts like mortality rates, the general public’s perception of risk depends more on a range of psychologi­cal and cognitive processes.

We can’t wish this away; humans are hard-wired to assess risk in complex ways, with different parts of the brain setting off different kinds of alarm bells. But we aren’t helpless, either. There are lessons for both policy-makers and the public at large.

For public health experts and political leaders, it’s important to recognize how the public assesses risk, and to appreciate that just citing numbers isn’t enough. As Slovic summarized his conclusion­s: “Those who promote and regulate health and safety need to understand how people think about and respond to risk. Without such understand­ing, well-intended policies may be ineffectiv­e.”

For the rest of us, just being aware of how we’re likely to react can help. You can’t avoid emotional reactions. But it is possible to recognize that reaction, deal with it, and focus on the actual risks. And in this case the facts are clear: getting a shot, any of the ones available, is the rational choice.

Simply being a woman carries a higher risk of blood clots than the AstraZenec­a vaccine

 ??  ?? Health Canada says there’s a one-in250,000 risk of getting a severe blood clot from the AstraZenec­a vaccine.
Health Canada says there’s a one-in250,000 risk of getting a severe blood clot from the AstraZenec­a vaccine.

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