COVID-19 vaccines: What you need to know about side effects and risks

Here are your questions, answered:

Q: Are the vaccines safe?

A: The Moderna and Pfizer vaccines, the only ones authorized for public use in the U.S., appear to have the same types of adverse effects, called risk patterns, as those of other shots, such as, for example, the meningitis B and shingles vaccines.

“In terms of trying to put it in context and say, these vaccines have similar risk patterns to other vaccines that have been used for a while, I think that’s a fair assessment,” said Dr. Archana Chatterjee, dean of the Chicago Medical School and a member of the Food and Drug Administration’s panel of vaccine experts charged with reviewing clinical trial data and recommending the shots for public use.

“All vaccines have some local adverse events associated with them; injection site redness, tenderness, swelling, those things occur, we know that. And it’s the same with these vaccines. Typically, both the local and systemic adverse events would last for a day or two,” Chatterjee added.

Q: How do we know what kinds of side effects there are?

A: There are different sources of data for the vaccines.

One is a platform, established in 1990, that allows patients who received the shots or caretakers of those patients to report their side effects, called the Vaccine Adverse Event Reporting System. It’s limited in that it only contains info that people voluntarily submit.

The other uses data from a smartphone app called V-Safe that the Centers for Disease Control and Prevention set up just for monitoring reactions to the coronavirus vaccines. During the first week after getting the shots, V-Safe sends the patient a daily text message as a reminder to complete a brief survey about how he or she feels. The frequency of the check-ins dips to only once a week for five weeks. All reports of adverse reactions are sent to the CDC.

Q: How do the rates of negative side effects of COVID-19 vaccines compare to other common shots?

A: The side effects associated with the Pfizer and Moderna shots are comparable to, though slightly worse than, those of other vaccines.

For example, 24.1% of recipients of the first Moderna shot reported headaches, compared with 25% of those receiving the meningitis B vaccine, according to VAERS data.

The most common adverse side effects of the COVID-19 shots are headache, fatigue, dizziness, nausea, chills, fever, and pain at the injection site, according to the CDC.

One unusual side effect of the COVID-19 vaccines is difficulty breathing, which a relatively small share of recipients have noted, though it is unclear how many of those fully recovered or needed further medical attention.

Note that the VAERS data reflects the first roughly 22 million doses of vaccine administered out of the total 40 million-plus total doses administered since the rollout began in December.

“That’s just your immune system working, so that I don’t consider anything serious,” said Dr. Paul Offit, a virologist at the Children’s Hospital of Philadelphia and a member of the FDA’s panel of vaccine experts.

It appears that the side effects are more pronounced with the second dose of the Pfizer vaccine, according to data taken from V-Safe. For example, 7.4% of users reported fevers after their first dose of the Pfizer vaccine, compared to 25.2% who reported fever after the second dose.

Vaccine experts have likened the effects of the coronavirus vaccines to those of the vaccine to prevent meningitis B, normally given to adolescents, and the vaccine to prevent shingles, normally given to adults 50 years or older.

Q: What about serious problems?

A: There is some indication that the rate of serious reactions to the COVID-19 vaccines may be higher, but it’s unclear, given how quickly the rollout has taken place.

The VAERS platform keeps track of these “serious” adverse reactions, that is, ones that result in hospitalization, life-threatening illness, permanent disability, congenital anomaly or birth defect, or death.

There were 45 reports of serious adverse reactions to the COVID-19 shots per 1 million doses administered. Nonserious adverse events were more common, with 372 reports per 1 million doses administered.

In comparison, the rate of serious adverse reactions for the meningitis B vaccine is 15 reports per 1 million doses. The rate of serious reactions for the shingles vaccine is 40 reports per 1 million doses. The shingles vaccine was given to adults older than 50, making it a better point of comparison, given that the COVID-19 vaccines have been given only to working-age and older people.

The rate of serious adverse reactions to the COVID-19 vaccines is, in context, “minuscule,” Chatterjee said. She noted that there tend to be more bad reactions reported when a vaccine is first rolled out, meaning that as more shots are administered, the rates should decrease.

Q: What about severe allergic reactions?

A: Reports of severe allergic reactions, or anaphylaxis, to the coronavirus vaccines are rare, CDC data shows. Reporting in VAERS shows that for every 1 million doses of the Pfizer vaccine administered, only five cases of anaphylaxis occurred. For every 1 million doses of the Moderna vaccine administered, 2.8 cases of anaphylaxis occur.

The risk of anaphylaxis is higher for the meningitis B and shingles vaccines. The rate of anaphylactic shock in each dose of the meningitis B vaccine is 6.16 cases per 1 million doses. Meanwhile, for every million doses of the shingles vaccine, 6.58 cases of anaphylaxis occur, according to a 2018 report published in the Journal of Allergy and Clinical Immunology.

Cases of anaphylaxis usually occur within 30 minutes of receiving the vaccine, which is why healthcare providers who give the shots keep the recipients under observation for about half an hour.

Q: What about other reports of people dying?

A: Reporting in VAERS showed that 129 nursing home residents who had received either the Pfizer or Moderna shots died within a few days. However, the CDC determined from these reports that the vaccines were not directly linked to any deaths.

“Deaths in [long-term care facility] residents following COVID-19 vaccination are consistent with expected all-cause mortality in this population,” members of the CDC Advisory Committee on Immunization Practices said in their most recent meeting in January.

The vaccine recipients who died were either very old and already sick with chronic diseases such as heart disease and kidney failure. For instance, one report from a healthcare provider said that at the time of infection, a coronavirus outbreak was underway in the patient’s nursing home.

“She had a number of chronic, underlying health conditions. The vaccine did not have enough time to prevent COVID-19. There is no evidence that the vaccination caused the patient’s death. It simply didn’t have time to save her life,” the healthcare provider reported to the VAERS platform.

In another report to VAERS, a caretaker said that her grandmother died a few hours after receiving the second Moderna shot but said they “don’t expect that the events are related,” but the hospital treating their grandmother “did not acknowledge this, and I wanted to be sure a report was made.”

“The adverse events that have been reported associated with these vaccines, both through the clinical trials and … now through the vaccine adverse events reporting system, have not raised concerns about any increased or different adverse event profiles that we see with other routinely administered vaccines,” Chatterjee said.

The CDC has been working with vaccine manufacturers to investigate the reported deaths. Pfizer announced last month that the company is “actively investigating” the recent death of Miami Beach gynecologist Dr. Gregory Michael, 56, after he received a dose of the Pfizer vaccine. He had developed an unusual blood disorder and died 16 days later. The CDC said that it would “evaluate the situation as more information becomes available and provide timely updates on what is known and any necessary actions.”