Side effects from the COVID-19 vaccine means 'your body responded the way it's supposed to,' experts say

·5 min read

Americans will likely experience at least one side effect from the COVID-19 vaccine, but doctors say that’s normal and you should still get vaccinated.

In Moderna’s Phase 3 trials, the company said the most common side effects were fatigue, muscle soreness and aches, joint pain and headache, plus pain, redness or swelling at the injection site.

More than half of Moderna’s study participants had side effects from the vaccine in Phase 1 trials, according to a preliminary report published in July in the New England Journal of Medicine.

In Pfizer/BioNTech Phase 3 trials, the probability of fatigue or headaches was 3.8% and 2%, respectively.

Experts say we’ll know more details about who is more likely to experience what side effects when the U.S. Food and Drug Administration finishes reviewing the Phase 3 trial data for both vaccines and releases that information to the public. The earliest that could happen is Dec. 10.

Physicians emphasize that the side effects are not just normal but also a sign that the body is reacting properly to the vaccine.

Dr. Melanie Swift, an occupational medicine physician helping lead the COVID-19 vaccination plan at the Mayo Clinic, said it’s important to educate Americans about a vaccine's side effects or it may deter people from getting a second dose as needed.

“Just because you’re sore doesn’t mean that (the vaccine) didn’t work or wasn’t effective. It just means that your body responded the way it’s supposed to,” she said. “It’s important to take both doses, or that first dose was all for nothing.”

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Side effects are not adverse events

Though companies and agencies tend to interchange the terms “side effects” and “adverse effects," experts warn that "adverse events" are a very different experience.

Side effects are common and don’t disrupt daily life. Adverse events are more unanticipated effects of a drug. Some adverse events from other vaccines reported over the decades include rare neurological events or vaccine-induced immune enhancement, said Dr. Len Horovitz, pulmonary specialist at Lenox Hill Hospital.

But while 10% to 15% of patients who get the flu vaccine experience side effects, Swift said adverse events likely occur in under .1% of patients.

“Adverse events are rarer events. … Side effects are common, self-limited and benign,” Horovitz said. Most side effects can be treated with a Tylenol, he said.

For example, if you work out at the gym and leave feeling sore, that's a common and expected side effect, Swift said. But if you leave the gym and get pink eye, that's a reportable adverse event. And if enough people get pink eye, then there's a problem with the gym.

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If someone is going to have a bad reaction to a vaccine, it is likely to occur in the first six weeks after vaccination, according to medical experts. But experts still don’t know the long-term effects of the COVID-19 vaccines and won’t know until after the trials are completed and researchers monitor participants in the real world for years after.

Drug and Safety Monitoring Boards for both Pfizer and Moderna reported no serious safety concerns for their vaccines. If there was an adverse event, Swift said, the board would have likely halted the trial.

That happened to Johnson & Johnson in October when its large-scale COVID-19 vaccine trial was paused after an unexplained illness in a volunteer. Another trial, run by AstraZeneca, was halted Sept. 8 after a participant in the U.K. was diagnosed with a neurological condition, believed to be transverse myelitis.

Both trials resumed after regulators found no evidence the vaccines caused the volunteers to fall ill.

“We have an extremely high standard for safety and adverse events,” Swift said, adding that Moderna and Pfizer probably would not have been able to submit their vaccines for FDA authorization if an adverse event were reported during trials.

CDC adds an extra layer of safety monitoring for COVID-19 vaccine

The U.S. Centers for Disease Control and Prevention has national monitoring systems in place to track reportable adverse events from vaccines. However, the agency added another layer of safety monitoring for the COVID-19 vaccine: V-SAFE.

It’s a new smartphone-based, post-vaccination health checker for essential workers who receive the vaccine. For those who enroll, the program will use texting messaging and web surveys to check in with people for health problems after vaccination.

The CDC said it plans to enroll up to 20 million people during the first few months of the program. Text messages and emails will be sent daily for the first week after vaccination and then weekly for six weeks.

The agency will not only ask about side effects and possible adverse events but also will ask about coronavirus infection to better understand effectiveness and how long vaccine protection may last.

Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

This article originally appeared on USA TODAY: COVID vaccine side effects: Headache, fatigue, aches are normal

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