Here Are All the Side Effects of Every Top COVID-19 Vaccine in US

Prepare for fevers, headaches and pain in the arm.

Heather Lieberman (L), 28, receives a COVID-19 vaccination from Yaquelin De La Cruz at the Research Centers of America in Hollywood, Florida, on August 13, 2020. CHANDAN KHANNA/AFP via Getty Images

Everyone is anxiously waiting for a COVID-19 vaccine. But as the world’s most cutting-edge drugmakers race towards the finish line, things have gotten complicated.

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In the U.S., there are four companies that are in the final stage of testing their COVID-19 vaccines: Moderna, Pfizer, AstraZeneca and Johnson & Johnson. All of them have reported side effects in trial participants after giving the shots. Two companies—AstraZeneca and Johnson & Johnson—have paused phase 3 human testing in the U.S. after several volunteers fell so ill that it worried health regulators.

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It’s not uncommon for vaccines to induce adverse responses in healthy people. Most of them will still make it past the FDA as long as the discomfort is mild and temporary. Yet, it’s something the public needs to know before taking any vaccine, especially one for a highly contagious virus like COVID-19, which would require vast adoption to stem its spread.

Moderna: chills, fevers, headache, shortness of breath, pain in the arm

Last month, Luke Hutchison, a 44-year-old volunteer in Moderna’s phase 3 trial, said he’d had a mild fever after taking the first shot of Moderna’s mRNA-1273 vaccine, and “full-on COVID-like symptoms” after the second shot.

Another volunteer, Jack Morningstar, a college student from the University of North Carolina at Chapel Hill, said he’d experienced fatigue after the first dose and a fever after the second. However, because the trial was double-blind, he wouldn’t know if he got the real vaccine or just placebo until the vaccine cleared FDA authorization.

Two other participants in Moderna’s study experienced similar side effects, according to CNBC. But they declined to go on the record. Hutchinson said he decided to go public about it because he was concerned that Moderna might not fully inform the public about its vaccine’s potential side effects.

Pfizer: fever, fatigue, chills, redness and swelling

Last Wednesday, Pfizer said in a report that some participants in the company’s late-stage trials had experienced mild side effects after getting the first shot of the vaccine and that fewer participants reported side effects after taking the second shot.

“Systemic events (fatigue, headache, chills, muscle pain and joint paint) were reported in small numbers of younger recipients of [the second shot],” Pfizer said in a report published in The New England Journal of Medicine. “But no severe systemic events were reported by older recipients of this vaccine candidate.”

Two trial participants said they experienced “slight flu symptoms” immediately after each of the two shots in August. A few volunteers in the younger group reported redness and swelling at the injection site.

The vaccine officially rolled out in the U.K. on December 8. After the first day of injection, Britain’s National Health Service (NHS) advised people with significant allergic reactions against getting the vaccine.

AstraZeneca: neurological disorder

At least two participants in AstraZeneca’s phase 3 trial experienced transverse myelitis, an inflammatory syndrome that affects the spinal cord, after receiving the company’s experimental COVID-19 vaccine.

The British pharma company halted testing globally last month after the first case of transverse myelitis was reported. On September 11, AstraZeneca published a report saying “there was insufficient evidence to say for certain that the illnesses were or were not related to the vaccine.”

The company has resumed phase 3 trials in the U.K., Brazil, South Africa and India, but not yet in the U.S.

Johnson & Johnson: unexplained illness

Johnson & Johnson paused its phase 3 vaccine trial (ENSEMBLE) last week after a volunteer experienced unexplained illness after receiving the shot.

The company didn’t disclose what the illness was due to privacy agreements with the participant. It’s also unclear whether the sick participant was in the actual vaccine group or in the placebo group.

“The participant’s illness is being reviewed and evaluated by the ENSEMBLE independent Data Safety Monitoring Board (DSMB) as well as our internal clinical and safety physicians,” Johnson & Johnson said in a statement. “Adverse events—illnesses, accidents, etc.—even those that are serious, are an expected part of any clinical study, especially large studies.”


This story has been updated as of December 9, 2020

Here Are All the Side Effects of Every Top COVID-19 Vaccine in US