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VERIFY: Yes, the COVID-19 vaccine might make you feel ill. That means it's working

The COVID-19 mRNA vaccines work by eliciting an immune response. That comes with some temporary side effects, like muscle aches or fever.

Pfizer and Moderna's COVID-19 vaccines are unlike any we've seen in the past. Instead of injecting people with a dead or weak version of the virus, like the flu shot, they use something called Messenger RNA, which trains the body to fight off coronavirus before ever coming in contact with it. 

Since the vaccine puts your immune system to work, a lot of people are asking whether getting the vaccine will make you sick. The Verify team brought that question to the experts.


Will the COVID-19 vaccine make you sick?


Yes, but that means it's working.



In a Verify story back in November, Dr. Paul Spearman helped us explain how an mRNA vaccine works, starting with what Messenger RNA is:

“It is a genetic code, basically, that is sort of ready and in someone's body to make protein,” Dr. Spearman said. 

Dr. Spearman said in the case of these vaccines, the mRNA has the blueprints for a protein of the coronavirus. It allows your muscles to start making these nasty proteins.

“The immune system sees it as if the person had been infected, but it's just that one little piece,” he said. “So the immune system reacts to it in a very desirable way.”

To break it down: mRNA vaccines give your body the genetic code of how to fight the virus.

An mRNA vaccine is designed to elicit a specific immune response in your body so it's ready to fight off the severe effects of coronavirus should you be infected. Dr. Barry Bloom says that's the reason you may feel sick for a few days after getting vaccinated.

RELATED: VERIFY: No, the coronavirus vaccines will not alter your DNA

"Virtually any vaccine that stimulates the immune response is going to produce a local reaction," Dr. Bloom said. "Any vaccine that contains RNA and encapsulated in lipids is very likely to stimulate an innate immune response."

Dr. Lisa Maragakis agreed and gave some examples of what this immune response could feel like.

"Vaccine developers report side effects that can include pain at the injection site, fever, muscle aches, fatigue and headaches, mostly lasting about a day or two," Dr. Maragakis told us via email. "If symptoms persist, you should call your doctor."

There have reportedly been four cases, two in Britain and two in Alaska, of people who received the Pfizer vaccine and experienced severe allergic reactions. Pfizer says they are monitoring and assessing these reports. They include the following guidance for vaccination providers:

"Appropriate medical treatment used to manage immediate allergic reactions must be immediately available in the event an acute anaphylactic reaction occurs following administration of Pfizer-BioNTech COVID-19 Vaccine."

Dr. Anthony Fauci, the nation's top infectious disease expert, explained that this is an example of the way that observations for safety don't end when clinical trials end.

"When the clinical trial gets its result, you have to keep monitoring for safety. And that's what's happening," Dr. Fauci says. "So what likely will be is that people who have a history of allergic reactions will be told either to not take this vaccine, or if you do take it, take it in a place where they're able to observe you, and if you do get an allergic reaction, to treat you right away."

You can watch the full interview with Dr. Fauci here:

RELATED: Fauci: March/April is when COVID-19 vaccine could be available to general public

The Verify team is keeping a close eye as more information and research is released pertaining to these allergic reactions.

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