COVID-19 Vaccines: How They Work, Side Effects & More

It's important for Americans to understand the differences between the available vaccines. As of March 1, 2021, there are COVID-19 vaccines authorized for distribution in the United States. They were also approved for emergency use by the U.S. Food and Drug Administration.

While all three have similar side effects, doses, time between shots and other elements vary between them. One of them functions much differently than the first two vaccines. Understanding these differences is part of the decision process when/if you sign up for an appointment.

Here's what you need to know about each available COVID-19 vaccine in the U.S.


Pfizer-BioNTech's vaccine, or just the Pfizer vaccine, was the first vaccine to become available in the United States.

It was made with recent technology where something called messenger RNA (mRNA) is injected into the recipient's body. This mRNA instructs cells to take a piece of COVID-19's "spike protein," triggering your immune system to fight the virus.

In clinical trials, the vaccine was 95% effective. You need two shots in a 21-day span — you get the first shot then 21 days later your return for the second — to gain the vaccine's full effectiveness. After you get the shot in the upper arm redness, swelling, and pain may happen at the injection site.

Possible side effects include fever, chills, tiredness, and headache, but this is more common after the second dose of the vaccine, according to the Centers for Disease Control (CDC). Most side effects varied from mild to moderate, the agency added. For the ingredient list, click here.


Moderna's vaccine functions the same as Pfizer's with the mRNA method. Compared to Pfizer, Moderna's effectiveness was 94.1% in clinical trials. You also need two shots to get the full effectiveness, but you have to wait 28 days in between your appointments.

You may also experience redness, swelling and pain where you got the shot. Possible side effects include fever chills, tiredness and headache, but these are more common after the second dose, according to the CDC. Most side effects were mild to moderate, they added.

"They might feel like flu symptoms and might even affect your ability to do daily activities, but they should go away in a few days," the agency said.

For the ingredient list, click here.

Johnson & Johnson

The Janssen vaccine developed by Johnson & Johnson was recently approved for emergency use by the FDA. This vaccine functions much differently from Pfizer's or Moderna's.

Unlike Moderna and Pfizer, Johnson & Johnson's vaccine requires one dose. The Janssen vaccine also injects a genetically engineered form of the common cold virus into a person's body. This altered virus infects cells and forces the body to build up the immune system, so when the coronavirus invades the body, it may be more equipped to fight it off.

Johnson & Johnson's vaccine had an overall efficacy of 66% with an effectiveness of 72% in the United States. It was 85% effective against severe cases of coronavirus in clinical trials.

If you get the Johnson & Johnson vaccine, you may experience pain, redness of skin and swelling at the injection site, according to the FDA. Possible side effects include headache, tiredness, muscle aches, nausea and fever. For the ingredient list, click here.

The COVID-19 vaccines are starting to become available across the country, and the Black Information Network wants to know if you plan to get vaccinated. Have you already gotten the vaccine? And what are your thoughts on the vaccine? Let us know! Click HERE to take our survey. You can also take the survey on your cell phone by dialing #250 and saying the keyword RADIO SURVEY. You’ll have the option to receive a one-time auto-dialed text message from iHeartMedia

Photos: Getty Images

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