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What to know about the Moderna vaccine

A bandage, a vaccine vial and a cotton swab.

A second coronavirus vaccine was OK'd for emergency use by the U.S. Food and Drug Administration (FDA) on Dec. 18, and the first doses began shipping out nationwide within days. This vaccine was developed by ModernaTX. (The first to be OK'd was developed by Pfizer and BioNTech.)

Here are some important questions and answers about this new vaccine.

Q. How does the vaccine work?

A. The Moderna vaccine contains genetic material called messenger RNA (mRNA). This small piece of the coronavirus's mRNA orders the cells in your body to make copies of the distinctive but harmless spike protein that appears on the surface of the coronavirus. These spike proteins trigger an immune reaction. Your body creates antibodies, which then protect you from getting sick if you're exposed to the real virus later.

It's important to note that the vaccine doesn't contain the real coronavirus. So getting the vaccine cannot give you COVID-19.

Q. How many shots are given and how far apart?

A. This vaccine requires two shots given one month apart.

Q. How long after getting your shots does it take to be effective?

A. According to the Centers for Disease Control and Prevention (CDC), it usually takes a few weeks for immunity to develop after any vaccine. Trial data suggest that this vaccine starts to offer some protection about 14 days after the first shot.

Q. How effective was the vaccine in clinical trials?

A. The vaccine was 94.1% effective in preventing COVID-19 in clinical trials. That's very good. FDA's benchmark was an efficacy rate of 50%.

It is not yet clear how long the vaccine will provide protection or whether it prevents someone from spreading the virus. So it will be important for those who get the vaccine to continue taking other safety precautions.

Q. What was its safety record in clinical trials?

A. Researchers looked at safety data broken down by:

  • Age.
  • Race.
  • Ethnicity.
  • Underlying medical conditions.
  • Previous COVID-19 infections.

There were no safety concerns. Serious adverse events occurred in similar numbers among people who got the vaccine and those who got a placebo.

Q. What were the most common side effects?

A. The most commonly reported side effects were:

  • Pain at the injection site.
  • Tiredness.
  • Headache.
  • Muscle pain.
  • Chills.
  • Joint pain.
  • Swollen lymph nodes in the same arm as the injection.
  • Nausea and vomiting.
  • Fever.

These side effects were more common after the second dose.

Q. Who is the vaccine authorized for?

A. The vaccine is authorized for people 18 years of age and older. There is not yet safety data available for children, pregnant women or people with weak immune systems.

Q. Who can get the vaccine?

A.
States set their own rules for distributing the vaccine. But CDC's Advisory Committee on Immunization Practices has recommended that healthcare workers and residents of long-term care facilities be the first to get the vaccine.

They recommend that it be made available next to: 

  • Frontline essential workers.
  • Older adults.
  • Younger adults with underlying medical conditions.
  • Other essential workers.

Check with your local health department to find out whether the vaccine is available to you yet.

Q. Who should not get the vaccine?

A. You should not get the vaccine if:

  • You have had a severe allergic reaction to any ingredient of this vaccine.
  • You have had a severe allergic reaction to a previous dose of this vaccine.

If you are pregnant or breastfeeding, talk with your doctor about whether to be vaccinated.

You can find more information about COVID-19 vaccines in our Coronavirus health topic center.

Reviewed 2/17/2021

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