Are COVID-19 Vaccines Safe?

A physician reviews the evidence of vaccine safety

Julian Willett, MD
Jan 9 · 7 min read
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The pandemic is scary and over one year into it, we are all exhausted. We want it to be over. While COVID-19 will likely remain with us for at least several more years, vaccines mean a semblance of normalcy will arrive sooner than this. The big questions are how these vaccines work and whether these vaccines are safe.

My Background

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I have an MD and am currently involved in COVID-19 genetics research in Canada (I earned my MD in the United States). Here is a similar article that I wrote on this topic, albeit for a different audience

The purpose of this article is to describe the vaccine in a simple manner so readers can make informed decisions regarding what they do or do not decide to put in their bodies. I make no assumptions regarding a reader’s science background.

What is an immune response?

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The inside of your body is like an always armed security alarm. The instant that something that is not supposed to be there is in your body like a splinter or bacteria, alarms go off. These alarms, the innate immune response, drives the release of SOS signals from the point of invasion, aka cytokines.

These SOS signals are sent along to central command so first responders can go out, ie the cytokines travel through the bloodstream driving activation of cells like neutrophils that go to the site. The first responders report to the site of invasion and do what they can to deal with the situation, such as eating up any invading organisms or walling off that nasty splinter so it is effectively contained analogous to being placed in the back of a police car.

Eventually, detectives will come along after a few days and try to better understand the situation, aka the adaptive immune response. They will write in their little pocketbooks all the evidence of what was left at the site of entry, ie macrophages or helper T cells collecting antigen, and bring it back to HQ.

They will then put on a massive presentation to all the other detectives at HQ that recognize the invader. Given that there could be an ulterior motive behind that pesky splinter, all the detectives start doubling their efforts by hiring aides and assistants so they will all be ready if the splinter strikes again.

As one would imagine, this mobilization of resources takes time so it can take several weeks to have enough resources in place to be ready for another attack of that splinter. When it happens again, the department will be more prepared so if the splinter and its pesky bacteria strike again, they will be able to react more quickly and better protect the house.

Where Vaccines come Into the Picture:

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Vaccines are like a bulletin made available to the detectives before any incident occurs at all. Imagine the detectives learning that a suspicious splinter has recently moved to the area and they have time to have resources ready in case anything happens.

If the splinter strikes, they will be more ready to engage and neutralize the threat. Considering SARS-CoV-2, the virus that causes COVID-19, the vaccine provides a bulletin to HQ of what the virus looks like. This way, they can be prepared in case the virus strikes.

For viruses that slide open your window rather than smash it, this preparation can prevent any damage at all. Think those detectives catching the virus in the act of entering the house and stop it before anything happens. For viruses that instead are more likely to smash a window in and cause more damage, the preparation prevents excessive damage from occurring. Think of those detectives finding the window broken in, but they stop the virus from causing more severe damage like clogging up the central air ducts.

Vaccine Safety:

All want to be as safe as possible from anything that could harm us. This thought very understandably would apply to vaccines as well. If I were to receive a vaccine, I would like to know if those detectives will only need to take a look around the house a bit to do their job or whether they need to do something more drastic.

Fortunately, the COVID-19 vaccine only involves those detectives taking a look around the house. It is impossible to get COVID-19 from the vaccine because the only thing that it gives to the detectives is a big picture of what they need to watch for rather than an inactivated or less dangerous form of the virus, think virus wheeled up in a straitjacket. That picture provides all the information the detectives need to be ready to keep you safe given enough time to prepare, typically 3–4 weeks.

There is an understandable concern of potential reactions one can have to the vaccine. It is extremely rare for the detectives to start a fire in your house, ie cause an anaphylactic reaction that could require hospitalization. This can be caused by the rare situation when one of the detectives has an irrational fear of cats and the cat that was previously locked in the bedroom because of visitors somehow got out, ie potential allergic reaction to a different compound in the vaccine called polyethylene glycol (1).

Fortunately for that jumpy detective, the cat only gets out in one out of one million houses (1). So in 999,999 houses, the cat does not get out and there is no allergic reaction. While the risk is not zero, a therapist is always available outside for that poor detective in case the extremely unlikely occurs. Patients are required to be observed for fifteen minutes after receiving their vaccine for any reactions that can be effectively medically managed on the spot (2). Thirty minutes if someone has had a reaction in the past (2). So you are more likely to get struck by lightning than have a reaction to the vaccine as for that, two houses out of a million will have the cat get out and frighten that poor detective (3).

As for other potential reactions, they are exactly as you are used to and expect. Most people have a slightly sore arm afterward with one in five taking something like Motrin or Tylenol to take the edge off (4). Of ten people who receive the vaccine, around four may get a bit tired that will go away likely after you sleep, around three may get a headache that will also improve with time and can be managed with Motrin or Tylenol, around two may have sore muscles that will also get better and can be controlled, around one may have chills (that get better), and one may feel a little nausea that will go away and can be controlled by anti-nausea medication (4).

The reasoning that I am getting from reading all of this information myself is that there is not much risk in taking the COVID-19 vaccine and a whole lot of benefit. Not dying and putting my family through that is a pretty big plus. While it is not perfect in that of 100 people who receive the vaccine, 5 people could still get it, 95 people being protected completely from getting it are very nice odds (5).

Even for those five people, their disease will be a lot less severe than what we are seeing right now with ICUs getting filled up with patients on ventilators. Not a good place to be considering oxygen is in shorter supply. I personally am looking forward to getting the vaccine and will be recommending it to everyone that I know.


The current pandemic is hard to deal with and scary. Vaccines have the potential to bring life back to something more resembling normal through providing our body’s detectives with pictures of the virus so they can more readily engage it and in the vast majority of cases prevent an infection from happening at all. It is very understandable to want to know if the vaccine is safe and that those detectives will not start any fires or get jumpy at the extremely rare unleashed cat.

Serious reactions to the vaccine are half as common as getting struck by lightning and the most common reactions are what you can expect from getting a shot, a sore arm that would feel better with some Motrin or Tylenol if you needed it.

While a sore arm is still unpleasant, the benefits are that after your body’s HQ has prepared enough for the virus, around 3–4 weeks after you receive the final dose of the vaccine, you will be greatly protected and less likely to get sick from the virus that has already taken the lives of over 1.9 million people (6). There are not many downsides to this marvel of medicine and I personally will be pursuing it and recommending it to everyone that I know.

Disclosures Statement:

I have no conflicts of interest to disclose. This article is meant for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.


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Julian Willett, MD

Written by

Loving husband. Physician scientist who enjoys spreading his knowledge with the world whether related to medicine, technology, or science.



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