Ounce of Prevention MD: Why Do We Have Side Effects to Vaccines?


Why Do We Have Side Effects to Vaccines?

At this point, everyone has read about the COVID vaccine, and I’m sure many of you are fully vaccinated by now. As more and more people become vaccinated, we’re reading stories in the news about “significant” side effects to the vaccines. About a third of everyone who gets the COVID vaccine has a side effect beyond just pain at the vaccine site. Most of these are “mild” (which in medical terms means “not hospitalized”), but they can feel very severe. These reactions have, understandably, made some people apprehensive to get the vaccine. However, mild side effects to vaccines are common, and can be considered a positive reaction. But why do vaccines cause side effects?

Understanding Side Effects

First, to understand why we have side effects, we need to understand a little immunology.  When you get sick from an infection, it’s not the infection that makes you sick, it’s your reaction to the infection that makes you sick. If your immune system detects an infection, it releases many compounds, such as interferon, interleukin, and tumor necrosis factor (TNF).

These compounds rev up your immune system to fight off the infection. But they can also make you feel sick. They cause your body to mount a fever, which you can survive, but bacteria and viruses typically can’t. In addition, these chemicals cause you to feel tired, achy, and nauseated, making you want to lie down and reserve your calories for fighting off the infection, rather than use your precious energy for digestion or exercise.

Source: Centers for Disease Control and Prevention

We’re Talking About Practice?

Vaccines are designed to simulate an infection, which can also cause the release of these immune compounds. Immunizations are basically practice for your immune system. They work by preparing your immune system for a specific bacterial or viral infection by presenting an “antigen”, which is a part of the infectious agent that triggers your immune system, but cannot cause the disease. Once presented with an antigen, your body makes antibodies that match the antigen and “remember” if that infectious agent ever shows up again. In other words, vaccines are actually the safest and most natural way to fight infection, because they rely on your body’s own defenses, rather than on medications.

Because vaccines use the same antigens found on bacteria and viruses, it’s not uncommon to have similar symptoms after a vaccine as you would to the actual infection. For instance, tetanus infection causes painful muscle contractions, so it’s common to have a painful shoulder muscle for a few days after you get a tetanus shot. Influenza causes fever and fatigue, so these can be reactions to a flu shot, albeit in a milder form. The COVID vaccine can cause headache, fatigue, fever and joint aches, which are common symptoms of COVID. This can explain the common misperception that vaccines can actually cause the illness they are designed to prevent.

The important point to remember is that a vaccine is supposed to cause an immune reaction, so feeling ill after a vaccine can actually be a good sign. It implies that you are building immunity, and are having the desired response. So feeling a little sluggish for a few days means you are far less likely to get a more severe illness later on. This also explains why you might have a more notable reaction after a booster shot, since you already have some immunity built from the first shot. However, if you don’t get any symptoms after a vaccine, you still likely have immunity, but are lucky enough not to feel side effects.

Side Effects May Include…

There are rare cases where a side effect to a vaccine can be severe and dangerous, but these are extremely unlikely. For example, the rate of anaphylaxis due to the COVID vaccine is about one in 100,000, which is far less than your risk of becoming seriously ill from COVID itself. Also, there is a condition called Guillain-Barre, which only occurs in about one in a million. You’re twice as likely to get hit by lightning than to get this condition from a vaccine!

It’s important to remember that you are not immune for a few weeks after you complete a vaccine series, so continue to take precautions to prevent infection. Also, if you get severe symptoms, such as shortness of breath or high fever, or symptoms last for more than 2-3 days, you should contact your physician.

Benefits Outweigh The Risks

Unfortunately, these side effects often get more press than the benefits of the vaccine, which causes some people to be hesitant to get immunized. One case of a serious illness makes for good news, but thousands of people staying healthy does not. The rule of thumb in medicine is that the benefits of any action should outweigh the risks. The benefits of vaccines far outweigh the risks, possibly more than any other prevention or treatment we have ever developed.  Vaccinations have essentially eliminated polio, smallpox, measles, mumps, and likely soon, chicken pox. They can also help prevent certain cancers, such as cervical and liver cancer, and, in the case of the flu vaccine, can prevent heart attacks and pneumonia.

So I urge you to get your COVID vaccine when possible, and any others for which you might be eligible. And if you get some mild side effects, take some Tylenol and feel confident and encouraged by the fact that it likely means the vaccine is working. A little misery now can save you from a lot of misery later!

Also, be sure to check out my upcoming town hall appearance on Wednesday, 3/16/2022, as I join Dr. Cecily Havert and Dr. Natasha Beauvais for a conversation on behavior change, habit forming (and breaking), and much more. Click here for event details.

Good luck, good health, and stay safe!

Ken Zweig, M.D.

Northern Virginia Family Practice

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