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Assessing the risks of vaccine side effects

People should be more afraid of the virus and its consequences because even those who survive can suffer long-term disabilities.

This article was first published in the Montreal Gazette

There are multiple reasons why people don’t get vaccinated. The reason I hear the most is the fear of side effects. Personally, I think people should be more afraid of the virus and its consequences because even people who ultimately survive can suffer long-term disability and are not the same after the experience. But news reports about side effects are understandably scary, particularly when they involve heart damage or neurological complications.

Quite a few people have been worried about side effects like Guillain-Barre Syndrome (GBS), a neurological condition that can happen to some people after vaccination. What we often forget is that GBS can also happen after bacterial or viral infections, too, and the risk of GBS post-vaccination is lower than it is after infection. GBS happens when something triggers the immune system to damage the peripheral nerves and results in a weakness that starts in the legs and moves up the body as the disease progresses. Fortunately, it is a temporary problem that often resolves on its own with most people returning to normal. In rare cases, people need to receive intravenous antibodies as a treatment but the prognosis is generally a good one.

But reports of GBS occurring post-vaccination have scared some people away from being vaccinated. Unfortunately, when people discuss vaccine side effects they often fail to put the risks in proper context. A recent study in the Journal of the American Medical Association measured the actual risk of GBS post-vaccination and found it to be very low. They modelled a few different scenarios, but even their “worst-case” scenarios found that the rate of GBS was only about eight cases per 100,000 person-years. The authors also added an important and often overlooked caveat that at least some cases of GBS must be due to other causes and part of the “background rate” of the condition. So if we would normally expect to see two cases of GBS per 100,000 person-years, only about six cases per 100,000 person-years can be attributed to the vaccine.

While this risk is very low, another point should provide extra reassurance. When GBS occurs it usually occurs soon after vaccination and not something that develops down the road. Even more importantly, the risk of GBS was particularly tied to the Johnson & Johnson vaccine and not to the Pfizer or Moderna vaccines, which are the ones mostly being used right now. As such it should not be a worry or a reason to go unvaccinated for most people.

Another common concern is the fear of Bell’s palsy, another neurological problem that can result in a facial paralysis that is also usually temporary and generally leaves no lasting damage. Worries about Bell’s palsy were raised when the initial studies of the Pfizer and Moderna vaccines found four and three cases of Bell’s palsy, respectively, in a combined group of about 35,000 people. These were likely chance findings and the risk was counterbalanced by the obvious benefit of vaccination. Still, the possibility was concerning to some. But subsequent research has not confirmed that any real link exists, and two studies from Israel and Hong Kong have not shown any significant increased risk. Interestingly, the Hong Kong study showed an increased risk with the CoronaVac vaccine (which is not being used in Canada or the U.S.) but not with the Pfizer vaccine.

In short, no one who has yet to be vaccinated has much to worry about with respect to these two conditions. The risk, if real, is extremely low and largely associated with vaccines that are not widely used in Canada. Too often we talk about side effects without acknowledging how rare they are and people assume that the risks with one vaccine apply to all vaccines, which is not true. People are understandably concerned about side effects, but in almost all cases that fear is unjustified.


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