Safety & Side Effects

COVID-19 Vaccine - Safety & Side Effects

Below are frequently asked questions related to COVID-19 vaccine safety & side effects. Click on another category to the left to see more FAQs.

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The FDA has confidently said that the Pfizer, Moderna and Novavax vaccines are safe. The Pfizer and Moderna vaccines are fully approved, and the Novavax vaccine is approved for emergency use. People who receive the vaccine will be monitored to check for safety, and participants in the original clinical trials will be followed for two years.

We understand there may be skepticism about the COVID-19 vaccine, especially among people of color, because of historical medical racism and experimentation in people of color. The COVID-19 clinical trials included people of all racial and ethnic backgrounds, and the vaccines were found to be safe and effective for all participants.

EUA is a way for the FDA to make vaccines and treatments available to the public under emergency circumstances, such as a pandemic.

Both EUA and full FDA approval are rigorous processes that look at the safety and effectiveness of the vaccine in tens of thousands of study participants.

One key difference is EUA looks at just two months of data from phase 3 clinical trials. Full FDA approval reviews at least six months of data.

All of the authorized vaccines work by helping your body produce antibodies. Antibodies are proteins that help fight infections from viruses, bacteria and other germs. Mild symptoms are common as when the body produces antibodies, and are not a sign of infection.

In ongoing clinical trials, the most common side effects included:

  • Pain at the injection site
  • Fatigue
  • Headache
  • Muscle pain
  • Chills
  • Joint pain
  • Mild fever

Side effects are generally mild and went away after a day or two. For the Pfizer and Moderna vaccines, they are likely to be more pronounced after the second shot.

While no longer approved or distributed, the CDC identified a plausible causal relationship between Johnson & Johnson/Janssen COVID-19 vaccine and blood clots with low platelets (thrombosis with thrombocytopenia syndrome, or TTS). TTS is a rare but serious adverse event that happens at a rate of about 3.83 cases per million doses. If you received the Johnson & Johnson vaccine and experience any sign of a blood clot or low platelets, including severe headaches, abdominal pain, leg pain, shortness of breath, or easy bruising or tiny blood spots under the skin beyond the site of injection, contact your doctor or seek medical care immediately.

Yes. Mild adverse reactions, such as soreness at the injection site, body and muscle aches, fatigue, and mild fever, are common. Serious adverse reactions may occur but are very rare.

Of the millions of COVID-19 vaccinations that have now been given in the United States, there have been a small percentage of adverse reactions reported through the Vaccine Adverse Event Reporting System (VAERS).

All UCLA Health facilities providing COVID-19 shots have staff with proper training and resources to care for those that experience adverse reactions.

No, but you should not get the COVID-19 vaccine if you have had a severe allergic reaction to any ingredient in the vaccine or if you had a severe allergic reaction to a previous dose of the vaccine.

Below is some additional information and context.

  • Between Dec. 21, 2020 and Jan. 10, 2021, more than 4 million first doses of the Moderna COVID-19 vaccine were administered in the United States.   
  • Within this group, 1,266 adverse events were submitted to the Vaccine Adverse Event Reporting System (VAERS), representing 0.03% of vaccinations.
  • From this list, 108 were identified as possible cases of severe allergic reaction, including anaphylaxis.
  • Of these case reports, 10 cases were determined to be anaphylaxis, including 9 in people with a documented history of allergies or allergic reactions, 5 of whom had a previous history of anaphylaxis. This represents a rate of 2.5 anaphylaxis cases per million Moderna COVID-19 vaccine doses administered.

All UCLA Health facilities providing COVID-19 shots have staff with proper training and resources to care for those that experience adverse reactions. Please talk to your doctor if you have additional questions.

If you take aspirin, acetaminophen (e.g., Tylenol) or ibuprofen (e.g., Motrin, Advil) for a medical reason, you can continue to take it as directed. However, we suggest that you do not take any of these medicines before getting your vaccine shot because they could dull your body’s immune response.

If you have a fever or body aches after being vaccinated, you may take these medicines as needed.

It is better to get vaccinated. Getting the actual COVID-19 disease is much worse.

When the virus that causes COVID-19 infects a cell, it injects all of its own genetic material into the cell and begins replicating itself. Contracting the virus can cause both direct damage to cells and inflammation, which can harm your entire body.

With the vaccine, your body gets instructions to build antibodies that keep the spike protein from ever infecting your cells.

Yes. Any type of vaccination can impact mammography results. Here's what you need to know:

  • When you get the COVID-19 vaccine or any other vaccination, the normal immune response may cause you to develop swollen lymph nodes under the arm in which you received the vaccine injection.
  • Swollen lymph nodes under the arm can be seen on a mammogram and can be a rare sign of breast cancer.
  • Swollen lymph nodes from a vaccination are normal and likely to normalize after about four weeks.

Based on this information, the current recommendation from the Society of Breast Imaging is that anyone due for a screening mammogram either schedule it before their COVID-19 vaccination or at least four weeks after vaccination. If that isn't possible, just let your make sure to let your doctor know when you received your COVID-19 vaccination so they can note that information on your medical record.