Fact Check-Vaccine side effects are not an indication that your body has been poisoned

Common side effects experienced by COVID-19 vaccine recipients, and recipients of vaccines more generally, are not signs that one’s body has been poisoned, contrary to social media claims.

A post shared here by the Facebook page “People Over Politics” says “SIDE EFFECTS ARE YOUR BODY’S WAY OF TELLING YOU IT’S BEEN POISONED IT IS NOT AN INDICATION THAT THE VACCINE IS WORKING.” Other posts making this claim can be seen here , here and here .

Both the United States and the United Kingdom have authorized the Pfizer/BioNTech and Moderna mRNA vaccines for emergency use, while the former has also authorized shots by Johnson & Johnson; Britain has also authorized the one by Oxford/AstraZeneca.


Both the Moderna and the Pfizer-BioNTech vaccine use new messenger RNA (mRNA) technology, which contains instructions for human cells to make proteins that mimic part of the novel coronavirus. The instructions spur the immune system into action, turning the body into a virus-zapping vaccine factory. No actual virus is contained in the vaccines (here).

These mRNA vaccines target the crown-like spikes on the surface of the coronavirus that it uses to break into healthy human cells. The spikes also give the family of viruses their distinctive name.

According to data from a real-world U.S. study released in late March 2021, COVID-19 vaccines developed by Pfizer and Moderna reduced risk of infection by 80% two weeks or more after the first of two shots (here).


The AstraZeneca shot meanwhile is a “viral vector vaccine”, where a specially engineered virus that normally causes chimpanzees to get the common cold delivers genetic instructions to human cells to make the spike protein jutting out from the new coronavirus’s surface (here).

The one-shot J&J vaccine likewise involves a more conventional approach, using a common cold virus to introduce coronavirus proteins into cells to trigger an immune response (here).


As stated here in a Reuters comparison of the side effects and potential risks of the COVID-19 vaccines, less than one in 10 people who receive the Pfizer-BioNTech vaccine experience swelling and redness at the injection site as well as nausea, while more common side effects are pain at the injection site, fatigue, headache, muscle pain, chills, joint pain and fever. The U.S. Food and Drug Administration (FDA)’s full briefing document for the Pfizer vaccine clinical trials that involved tens of thousands of volunteers is available here .

Similarly, less than one in 10 recipients of the Moderna vaccine experience rash, redness or hives at the injection site, while more experience pain or swelling at the injection site, tenderness and swelling of the underarm glands, headache, nausea, vomiting, muscle and joint aches, stiffness, fatigue, chills and fever. The FDA’s full briefing document for the Moderna vaccine is available here .

As for AstraZeneca, less than one in 10 people experience swelling, redness or a lump at the injection site, vomiting, diarrhea and flu-like symptoms. More than one in 10 face tenderness, pain, warmth, itching or bruising where the injection is given, fatigue, chills or feeling feverish, headache, nausea, joint pain and muscle ache. Published in The Lancet, data on the efficacy and safety, including side effects, of the AstraZeneca vaccine can be found here .

Less than one in 10 Johnson & Johnson recipients experience fever, redness and swelling at the injection site, while more than one in 10 experience pain at the injection site,

fatigue, headache, muscle ache and nausea. The FDA briefing document for this vaccine is available here .


As explained here by the World Health Organization (WHO), “vaccines are designed to give you immunity without the dangers of getting the disease,” which means it is normal to have side effects ranging from mild to moderate.

According to Dr. Melanie Swift, co-chair of Mayo Clinic's COVID-19 Vaccine Allocation and Distribution Work Group, a vaccine recipient experiences side effects because the “immune system is revving up and reacting”, just as it does when one gets sick (here).

With two-dose vaccines like the ones made by Pfizer and Moderna, side effects are often more intense with the second dose because the body has developed an immune response in the weeks since the first dose, meaning it is “ready to attack”, according to Swift.

“The second vaccine dose goes into your body, starts to make that spike protein, and your antibodies jump on it and rev up your immune system response. It’s kind of like they’ve studied for the test. And it’s acing the test.”


False. Common side effects from vaccines do not indicate that one’s body has been poisoned, but rather that one’s immune system is responding.

This article was produced by the Reuters Fact Check team. Read more about our fact-checking work here .