Your Questions About the COVID-19 Vaccine Answered: Part I

Annie Lamei, c2023

With the vaccines beginning to roll out, everyone has a lot of questions. As future health professionals, we often end up fielding questions from friends and family. This series aims to answer some of your questions and provides you with the resources to find the answers to the rest. If you have additional questions that you’d like to see answered in a future segment, please reach out to us at .

  1. What are the known side effects of the SARS-CoV-2 vaccine?

The known side effects of the SARS-CoV-2 vaccine are quite similar to the side effects of most other vaccines. Health Canada’s list of “pain at the site of injection, body chills, feeling tired and feeling feverish” should sound familiar to anyone who’s been keeping up with their flu vaccinations[1],[2].

2. How do we know the long-term side effects of a vaccine developed and tested within the past year?

This question usually arises when comparing the COVID-19 vaccine to pesticides and preservatives, whose negative impacts can often only be seen as cancers developing years later[3]. These concerns seem to make sense at first: with the earliest human vaccine trials starting in April-May 2020[4], it’s impossible to definitively track whether the vaccine has specific long-term risks.

Long-term consequences of vaccinations—even multiple vaccinations—are rare and unlikely to be clinically relevant[5]. In fact, this consistent lack of dangerous side effects is the reason why vaccine clinical trials are only required to follow their patients for thirty days before they can be eligible for licensing[6]. Of course, governments require doctors report any symptoms their patients experience that occur after this period[7]. Despite all this, the intense scrutiny on the COVID-19 vaccine has made Moderna and Pfizer decide to follow their clinical trial volunteers for at least several more years[8].

Even if the vaccine had the potential to cause harm, it has several key distinctions from the types of chemicals used in pesticides or harmful preservatives. In the words of Paracelsus, the dose makes the poison. Chronic exposure to a substance is more dangerous, and compared to pesticides, exposure to vaccines is not chronic (the substances in the vaccine are degraded by your body within a month)[9]. Even smoking just one cigarette in your entire lifetime is unlikely to cause relevant long-term effects[10]. Additionally, vaccine ingredients have not been determined to be harmful, with most found in everyday food items or even naturally in our bodies, whereas pesticides have confirmed harmful effects [11].

Despite all this, it would be incorrect to say that there is absolutely no way a COVID-19 vaccine could have adverse long-term effects. A tiny risk is still a risk, nonetheless. However, these risks must be considered against that posed by the virus itself. Beyond the risk of death, COVID-19 can cause long-lasting symptoms such as fatigue, shortness of breath, joint pain, chest pain, cough, loss of smell or taste, and a whole host of other symptoms, even in young, healthy individuals[12]. More severe long-term effects include organ damage (notably to the heart, brain, and lungs), increased predisposition to thrombosis, and even PTSD, depression, and anxiety[12]. Although we can’t know exactly what the vaccine will do in ten years, neither do we know exactly what COVID-19 will do ten years after the initial infection. I think it’s clear that the risks of COVID-19 far outweigh those of the vaccine—even in otherwise healthy individuals.

3. How does the vaccine work? Is it possible to get COVID-19 from the vaccine?

The two COVID-19 vaccines (Moderna and Pfizer) currently approved in Canada are both mRNA vaccines[13],[14]. To understand the mechanism of mRNA vaccines, we need to revisit the central dogma of biology. It states that DNA holds the “master copy” of all the genetic information in your body, while mRNA is a copy of the information contained in a small section of your DNA[15]. Copying this information into mRNA allows it to leave the protected environment of the nucleus, to interact with ribosomes and produce proteins. The proteins go on to achieve many functions that are critical to life.

The main ingredient of the mRNA vaccine is a modified version of the SARS-CoV-2 spike protein[16]. Anchored to the surface of the virus, the function of this spike protein is to allow the rest of the virus to be able to enter and infect your cells[17]. The vaccine includes only the spike protein mRNA and no other SARS-CoV-2 ingredients[16]. It will be your body’s own cells and ribosomes that translate the mRNA into isolated spike protein. Thus, your body is trained to recognize any pathogens with this spike protein and can produce a more rapid and effective immune response against the real coronavirus, should you be exposed[15].

Therefore, the vaccine cannot cause someone to be infected with COVID-19. There are a few rare cases of vaccines for other illnesses (not COVID-19) infecting patients with the disease. In most cases this has occurred with “live” vaccines, such as some polio vaccines[18]. Live vaccines work by injecting a weakened form of the virus, which has in some way been modified to be unable to cause disease[19]. However, some of the weakened virus may be able to mutate and revert to the infectious form, particularly in patients with weaker immune systems[20]. Fortunately, the COVID-19 vaccine is not a live vaccine, and so this is not a risk.

4. Will I need to be vaccinated against COVID-19 if I have already had the disease?

Unfortunately, it is possible to be re-infected with COVID-19[21]. This is because the antibodies generated as a result of infection with COVID-19 only last for around 40 days[22]. Health Canada is recommending that if you have recently had COVID-19 (i.e. if you had a PCR-confirmed infection within the last three months), then vaccination be delayed[23]. This is due to vaccine shortages—the consensus is that reserving the vaccine for those unlikely to already have immunity is a better strategy[23]. Restrictions will be lifted once the vaccine is more widely available[23]. Of note, getting vaccinated despite already having been infected with COVID-19 will not have any additional side effects.

If you currently have COVID-19, you should not be vaccinated until your symptoms resolve and your self-isolation period is over, regardless of vaccine shortages. You can find Health Canada’s complete list of recommendations here.

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