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A Project of The Annenberg Public Policy Center
SciCheck’s COVID-19/Vaccination Project

How safe are the vaccines?

This article is available in both English and Español

Hundreds of millions of doses of COVID-19 vaccines have now been administered in the U.S. and only a few, very rare, safety concerns have emerged. The vast majority of people experience only minor, temporary side effects such as pain at the injection site, fatigue, headache, or muscle pain — or no side effects at all. As the CDC has said, these vaccines “have undergone and will continue to undergo the most intensive safety monitoring in U.S. history.”

A small number of severe allergic reactions known as anaphylaxis, which are expected with any vaccine, have occurred with the authorized and approved COVID-19 vaccines. Fortunately, these reactions are rare, typically occur within minutes of inoculation and can be treated.

As of Jan. 18, there have been 2.5 cases of anaphylaxis per million doses of the Moderna vaccine and 4.7 cases per million of the Pfizer/BioNTech vaccine, according to a report by the Centers for Disease Control and Prevention. Those who develop anaphylaxis are usually given epinephrine, the drug found in EpiPens. None of these reactions has led to death. On Feb. 26, Johnson & Johnson said it had received a report of one anaphylactic reaction in South Africa.

To make sure serious allergic reactions can be identified and treated, all people receiving a vaccine should be observed for 15 minutes after getting a shot, and anyone who has experienced anaphylaxis or had any kind of immediate allergic reaction to any vaccine or injection in the past should be monitored for a half hour. People who have had a serious allergic reaction to a previous dose or one of the vaccine ingredients should not be immunized. Also, those who shouldn’t receive one type of COVID-19 vaccine should be monitored for 30 minutes after receiving a different type of vaccine.

The Johnson & Johnson vaccine has been linked to an increased risk of rare blood clots combined with low levels of blood platelets, primarily in women ages 18 to 49. Early symptoms of the condition, which is known as thrombosis with thrombocytopenia syndrome, can appear as late as three weeks after vaccination and include severe or persistent headaches or blurred vision, leg swelling, and easy bruising or tiny blood spots under the skin outside of the injection site.

As of July 12, the syndrome has been confirmed in 38 cases, after more than 12.8 million doses of the J&J vaccine. There have been three deaths linked to the condition, as of May 7, according to the CDC.

In April, the FDA and CDC recommended “a pause in the use” of the vaccine to investigate six reports of the syndrome out of more than 6.8 million immunizations. After a review, which turned up nine more cases, the CDC and FDA determined that the benefits still outweigh the risks and that the pause should be lifted. A warning was nevertheless added to the vaccine’s fact sheet and the CDC has said that women younger than 50 years old “especially should be aware” of the condition and that “that there are other COVID-19 vaccine options available for which this risk has not been seen.” The condition is still rare among the highest-risk group, occurring in around 7 of every million vaccinated adult women below the age of 50.

On July 13, the FDA added warnings to fact sheets on the J&J vaccine about an observed increased risk of the neurological disorder Guillain-Barré Syndrome.

The agency said the chance of developing the syndrome is “very low” but advised J&J vaccine recipients to seek medical attention if they experience symptoms including weakness or tingling, particularly in the legs or arms; difficulty walking or with facial movement; double vision; or bladder control or bowel function issues.

The warning came after preliminary reports of 100 cases, with most people reporting symptoms within 42 days of vaccination. One death was reported, but it isn’t known whether the death or the cases were caused by the vaccine. The FDA said that each year 3,000 to 6,000 people develop the syndrome and most recover fully.

There is emerging evidence that the Pfizer/BioNTech and Moderna mRNA vaccines may very rarely cause inflammation of the heart muscle (myocarditis) or of the surrounding lining (pericarditis), particularly in young men. In late June, after a review of safety monitoring data, the CDC’s Advisory Committee on Immunization Practices concluded there is a “likely association” between COVID-19 mRNA vaccination and the two conditions in teens and young adults.

As of July 12, the agency says there have been 1,047 preliminary reports of either condition in people 30 years old or younger following immunization with any COVID-19 vaccine. The bulk of the reports, which are through the Vaccine Adverse Event Reporting System and do not necessarily mean the vaccine caused the problem, are with the Pfizer and Moderna vaccines and are more common among males and after the second dose.

Health officials have emphasized that the potential vaccine-related myocarditis and pericarditis cases are rare and the benefits of vaccination still outweigh the risks. Early evidence, the committee said, suggests these myocarditis cases are less severe than typical ones. The CDC has also noted that most patients who were treated “responded well to treatment and rest and quickly felt better.”