Severe side effects from COVID-19 vaccination are rare

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Sick young woman lying on the couch taking some pills with a glass of water.

The most common reason people have not received a COVID-19 booster dose is concern about side effects, according to a recent survey of our readers. With eight reasons to choose from, 37% chose “I had side effects and I don’t want to go through that again.”

Some people worry the vaccine will cause them to miss a day of work or they don’t want to endure a fever or chills.

“My reaction to the second COVID-19 shot was not fun,” wrote one reader.

These types of side effects are common and indicate your body is building an immune response.

Other readers are concerned about more severe side effects, which are rare.

“The vaccine is quite safe and highly effective at reducing severe illness and death,” said Dr. Paul Cieslak, medical director for communicable diseases and immunizations at Oregon Health Authority (OHA). “One is definitely better off with it than without it. I got my vaccine and boosters, and I made sure that my family got vaccinated.”

The United States recently surpassed the grim milestone of 1 million COVID-19-related deaths. Recent CDC data show people who weren’t vaccinated were 17 times more likely to die from COVID-19 than those who received a primary vaccine series plus a booster dose.

Why does the vaccine cause side effects?

When we receive an mRNA vaccine (Moderna of Pfizer), it tells our cells to build copies of the spike protein found on the surface of the virus that causes COVID-19. It’s impossible for these spike protein copies to infect us with COVID-19. But our body sees a protein it doesn’t recognize and launches an immune response to build antibodies. That immune response comes with the common side effects many feel from the vaccine, and those side effects should go away within a few days.

“Reactions to the vaccine vary quite a bit from one person to another,” Cieslak said. “But regardless, we know that about 95% of people build an immune response to it.”

If you experience these symptoms, you can take over-the-counter medicine, such as ibuprofen or acetaminophen to help with discomfort. It is not recommended to take these medications before vaccination; take them only if you need them.

Adverse events following vaccination

Anaphylaxis is a severe allergic reaction that may occur within minutes after receiving any vaccination. For COVID-19 vaccinations, it has occurred at a rate of about five cases per 1 million vaccinations. Health care providers can effectively treat the reaction immediately, and this is why COVID-19 vaccination clinic workers ask people to wait at least 15 minutes before leaving. For more information on allergic reactions to the COVID-19 vaccine, including anaphylaxis, visit here.

Myocarditis is inflammation of the heart muscle, and pericarditis is inflammation of the outer lining of the heart. These reactions are rare and happen most often in teenage or young adult males, usually within one week of receiving an mRNA COVID-19 vaccination (*Pfizer or Moderna). Symptoms include chest pain, shortness of breath and a fast-beating, fluttering or pounding heart. Most patients respond well to treatment of their symptoms and feel better within a few days.

statistical chart showing verified cases of myocarditis for people under 18 in the US after receiving the COVID vaccine.

Myocarditis and pericarditis occur more often after the second dose of an mRNA vaccine primary series. To reduce the risk of heart complications, males ages 12-39 may consider waiting eight weeks after receiving their first dose to get their second dose.

As for booster doses, one reader from our survey expressed concern that “booster shots have a higher risk of complications like myocarditis. It seems that COVID is becoming less severe with the new Omicron variants, so I believe that the booster shot is of higher risk to me at this time than becoming infected with COVID.”

statistical chart on myocarditis occuring less often after a booster dose than after the second dose of a primary series in boys under 18

Additionally, data from 40 health care systems found that the risk of cardiac complications was significantly higher after SARS-CoV-2 infection than after mRNA COVID-19 vaccination for both males and females in all age groups, according to the CDC.

Thrombosis with thrombocytopenia syndrome (TTS) is a rare but serious adverse event that can result from receiving a Johnson & Johnson (J&J) COVID-19 vaccination. TTS causes blood clots in large blood vessels and low platelets (blood cells that help form clots). It has occurred in approximately four cases per  1 million J&J doses administered.

As of May 31, 2022, 586 million COVID-19 vaccine doses have been administered in the United States. Nearly 19 million of those were J&J. The CDC has identified nine deaths that may have been caused by the J&J vaccine. In most cases, mRNA vaccines are preferred to the J&J vaccine.

“Any vaccine or other medication has side effects, and COVID-19 vaccines are no exception,” Cieslak said “But serious side effects are rare, and life-threatening COVID-19 has been all too common. That’s why we recommend vaccination.”