How We Know the COVID-19 Vaccine is Safe

This blog was originally published on December 22. For the latest COVID-19 vaccination information, including which groups are currently eligible, visit our vaccine page.

There’s a lot of information about the COVID-19 vaccines to keep up with. In previous blog posts, we’ve explained the process of developing and authorizing the first COVID-19 vaccine for use, and who will get the vaccine first and why. You probably have questions about the safety of the vaccine. Here are the facts:

Safety during vaccine development and trials was a top priority

No phases of vaccine development or testing were skipped

All vaccines, when developed, go through trial phases. In those phases, the researchers recruit volunteers to try the vaccine. The phases help determine if the vaccine is safe and if there are any serious side effects. The COVID-19 vaccine process moved quickly, but no phases were skipped and were as rigorous as usual. In total, the Pfizer vaccine had over 44,000 volunteers participate in the trials and trial volunteers were monitored for a minimum of two months following vaccination.

Safety monitoring doesn’t stop when a vaccine is authorized or approved. The FDA and CDC closely monitor vaccine safety after the public begins to use a vaccine. They watch for possible side effects and adverse events. This ensures they identify any possible risks associated with the vaccine.

Volunteers were protected

After centuries of medical abuse in our country, there are now rules to ensure that companies and the US government do not test medical treatments on people without their consent. In order for a vaccine to be approved or authorized by the Food and Drug Administration (FDA), an Institutional Review Board (IRB) made up of researchers not connected to the vaccine assures that steps are taken to protect the rights and welfare of the people participating in the research.

Representation is important

The Pfizer and Moderna vaccine trials included people of various racial and ethnic groups. For the Pfizer vaccine in particular, approximately 42% of overall and 30% of US trial volunteers were non-white. In the Moderna trials, people of color made up around 37% of volunteers.

The vaccine is safe

No specific safety concerns were found

In the Emergency Use Authorization (EUA) for both the Pfizer and Moderna vaccine, FDA analysis of the vaccines says they found "no specific safety concerns identified that would preclude issuance of an EUA."

When looking at the incidence of serious adverse events for the Pfizer vaccine, it was extremely low, and similar for both the volunteers who received vaccine and those who received a placebo, at 0.6% and 0.5% respectively.

You can’t get COVID-19 from the COVID-19 vaccine

The Pfizer and Moderna vaccines that have been authorized don’t use the live virus that causes COVID-19. As a matter of fact, they don’t contain the virus at all.

About 30 years ago, scientists began developing a new kind of vaccine, using Messenger RNA (mRNA). When the pandemic began, scientists had already been hard at work on the new technology. They have used the gene structure of the virus to create the right mRNA sequence for the vaccine.

mRNA is not able to alter or modify your genetic makeup (DNA).

Former CDC director Dr. Tom Frieden explained it like this: mRNA is like an email that tells your immune system "what the virus looks like, instructions to kill it, and then – like a Snapchat message – it disappears." The CDC has more information about mRNA vaccines.

You may experience some side effects that seem like symptoms of COVID-19, like headache or fever after you get your vaccines. It doesn’t mean the vaccine gave you the virus. It’s normal, and it means your body is building immunity to the virus. This is a great explanation on how COVID-19 vaccines work.

Just like with a flu shot, it takes a little while for your body to build up full immunity after you get vaccinated. While you are waiting, you’re not fully protected and could actually get sick with the virus. This is part of the reason that it’s so important to keep doing all the protective measures you’ve been doing, like wearing a mask and washing hands often, even after you’ve gotten your vaccines.

Some side effects are to be expected

As we mentioned above, it’s normal to feel some mild to moderate side effects after you get your COVID-19 vaccine. It’s a sign your body is building up immunity to the virus.

The most common side effects include pain and swelling where you got the shot, fever, chills, tiredness, and headache. You may feel a little like you have the flu. It’s a normal reaction, and the side effects typically last just a day or two. The CDC has great information on what to expect for side effects and how to deal with them.

Unexpected adverse events get reported

We explained the normal possible side effects you may have after getting your vaccine. So what is an adverse event? In short, it’s any health problem that happens after someone gets a vaccine. It could be a true reaction to the vaccine, like a side effect, or it might be a coincidence that the health problem happened to occur after the vaccine was given, but isn’t caused by the vaccine. We like this explanation of adverse events from the CDC.

We explained earlier how the CDC and FDA will continue to monitor COVID-19 vaccines for safety concerns. Individuals are also encouraged to report adverse events. Safety of these vaccines is a top priority, and reporting adverse events helps the CDC monitor the safety of the vaccines. We like this explanation of the difference between a side effect and an adverse event, and encourage you to check it out.

Healthcare providers are required to report certain adverse events to a national system when they see them after providing vaccines. They also have to stick to any revised safety reporting requirements that are spelled out in the Emergency Use Authorization (EUA) of the vaccine.

The CDC is using something new to check in on your health after you get a COVID-19 vaccine. It’s a tool for your smartphone called v-safe. If you enroll to use v-safe, you can report adverse events or side effects and get a reminder for your second dose of the vaccine!

People with a history of severe allergic reaction

If you have a known history of a severe allergic reaction (anaphylaxis) to the components of the COVID-19 vaccine, talk to your healthcare provider about your risks.

Add COVID-19 vaccines to your pandemic toolbox

It’s important to use trusted sources of information when making health decisions. Websites like the CDC present the facts and are updated regularly as new information is known. We promise to keep you updated as we learn more!

Adding 2 doses of COVID-19 vaccine, when it’s available to you, is one more tool to add to the toolbox you’ve been using to protect yourself from COVID-19. Please be patient as vaccines are rolled out, and while you wait, use everything in your toolbox to keep yourself and your loved ones safe, including:; wearing a mask, washing hands often, keeping distance, avoiding gathering, and staying home with you’re sick. Just as we can’t build a house with just a hammer, we can’t end the pandemic with just one of these tools. We need them all to get there.