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  • Alex Cloherty

Long-term side effects

This week on Microbial Mondays, I am responding to a reader's question. She asked, "I keep hearing people say that they’re scared of getting a Covid vaccine because they’re concerned about ‘long term side-effects’. Is there evidence that any vaccine has had concerning long-term side effects?"

It is a great question! Indeed, with some vaccines, there are indeed very low risks of long term complications. However, across all modern vaccines, the most common side effects by far are short term and relatively manageable. For example, experiencing an allergic reaction, which may be due to a hypersensitivity to preservatives used to keep the vaccine safe up to the point at which it is delivered, is one of the more commonly talked about (although still very uncommonly experienced) side effects. However, this usually happens at the point of vaccination - within about 20 minutes of receiving the vaccine - and can thereby be treated at the doctor's office. Furthermore, pharmaceutical companies typically try to use the same or similar additives/preservatives across modern vaccines, so that it is easier to predict if individuals will experience an allergic response to a vaccine, based on their past medical history. Other common side effects are, for example, mild fever or mild abdominal discomfort. All of these side effects, whether they are long or short term, are taken very seriously, and there are national and international medical bodies that track them.

I think a lot of the fear from long-term side effects comes from historical incidents from back in the days where humanity was battling a host of deadly diseases all at the same time, and when we knew much less about vaccines. One such example is the so-called "Cutter Incident", named after the faulty vaccine produced by Cutter Laboratories in California.

Cutter Laboratories was producing the polio vaccine that had just recently been developed by Jonas Salk. This vaccine was based on "inactivated" - i.e. "killed" and non-functional - virus. The idea was, you would be injected with the non-functional virus, and your immune system would learn to recognize this safe version of the microbe, thereby protecting you from an eventual encounter with the live virus. However, two batches of the polio vaccine produced by Cutter Laboratories were not correctly inactivated, leading to people being accidentally and unknowingly injected with functional, live virus. This terrible accident, which occurred in 1955, was uncovered because even then there was a system of detailed reporting of all side effects or complications following vaccination. It was reported to local health authorities that, following vaccination, some of the patients injected with the vaccine, and specifically vaccine produced by Cutter Laboratories, developed paralytic polio that began in the vaccinated arm.

The Cutter incident is considered to be one of the worst disasters in the history of vaccines. In total, of the 164 people who developed paralysis in response to the vaccine, ten died. An additional 40,000 patients developed a milder form of polio that, luckily, did not affect their central nervous systems. However, you also have to keep in mind that in the case of polio, even with this horrifying disaster, the vaccine still saved countless lives. For comparison 1952, before the vaccine, over 3000 people died of polio in the United States alone, and there were nearly 58000 cases. Today, thanks to the vaccine, the World Health Organization has announced that there were only 94 cases of wild polio worldwide in 2019.

My point is, that people often forget that there is also a long-term risk of not being vaccinated. Choosing not to be vaccinated is also a choice that entails a risk - and typically when you are facing off against a vaccine-preventable disease like COVID-19 (or polio, mumps, chicken pox...), there is indeed a risk of long term complications upon infection. You are probably lucky enough to have never encountered the possibility of permanent paralysis due to an infection with the polio virus, thanks to Jonas Salk's vaccine. Because of the huge success of the MMR vaccine, you probably also haven't had to worry about an infection with mumps causing testicular atrophy (yes, literally your balls shrink, and your sperm count can be permanently reduced) or deafness. You might, though, have heard of shingles, an excruciatingly painful condition that results from re-activation of the chickenpox virus in adulthood. Shingles itself is a long-term side effect of chickenpox; if you had chickenpox as a kid, you have the potential to get shingles as an adult, because once you are infected with the responsible Varicella virus, it stays with you forever, lying dormant in your nerves. When you have shingles, you get painful blisters all over your body, and the most common long-term side effect of having shingles is so-called "postherpetic neuralgia" - i.e. long-term pain that stays with you even after your body-wide blisters have healed. You might at this point ask, what is the only way to prevent contracting chicken pox, and thereby potentially developing shingles? A vaccine.

You see, typically the risk of long term complications following infection is drastically higher and more serious than the risk of complications following vaccination. So to reiterate, this is not a choice for complications or lack thereof - it is a choice for a scientifically demonstrated higher (infection with the wild virus) versus lower (getting vaccinated) risk of harm.

To close, I totally understand being concerned about long-term health risks. It's great for people to think about them. I think about them all the time. But to get on the right side of statistics, you have to weigh your options rationally. My usual recommendation is that if people are truly worried about very small risks for long term health issues, they should stop eating processed meat, candy, and fast food, start exercising regularly, and make sure they always look both ways before crossing any street.

And, get vaccinated.

Until next week - eat your greens and get your jabs!

~ Alex

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