Why it might be best to avoid painkillers as a precaution before your COVID-19 vaccine

Billions of people worldwide will receive vaccines to protect against COVID-19 and some will temporarily feel a sore arm, fever or muscle aches. But reaching for some commonpainkillers could blunt the effect of the vaccine, experts say.

Mahyar Etminan, an associate professor of ophthalmology, pharmacology and medicine at the University of British Columbia, looked at data on taking medications like acetaminophen (Tylenol) and anti-inflammatories like ibuprofen (Advil, Motrin) before or close to the time of vaccination.

"Given that a lot of people would probably resort to using these drugs once they're vaccinated, if they still have aches and pains, I thought to put the data into perspective," said Etminan, who has a background in pharmacy, pharmacology and epidemiology.

The jury is out on what happens to aperson's immune system after aCOVID-19 vaccine if the person has taken those medications. But based on research on other vaccines like for the flu, there may be a blunting effect on immune response from the pills.

"If you tell people not to take them and they don't like the side-effects they're experiencing, that may lead to non-compliance with the second dose," Etminan said. "I think it is an important sort of question to look at scientifically and also to tell patients."

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Why might fever-reducing meds interfere with our immune response after vaccination?

It has to do with what's happening when our temperature rises to fight off an infection.

Dr. Sharon Evans, a professor of oncology at Roswell Park Comprehensive Cancer Center in Buffalo, N.Y., works on training the immune system to attack cancer. She became interested in fever because it is such a common response across animals that walk or fly, even cold-blooded ones.

Before the pandemic, Evans and her colleagues wrote a review on how fever generally helps to reduce the severity and length of illness.

Evans called fever "incredible" for its ability to boost all the components needed for a protective immune response.

Fever "literally mobilizes the cells, it moves them in the body into the right place at the right time," Evans said.

There's also good evidence that inflammation, even without fever, can boost immune responses, she said.

Fever pills generally not recommended before vaccines

In a preprint to be published in the journal CHEST, Etimanan and his colleagues noted that arandomized trial looking at infants given acetaminophen immediately following vaccination showed lowered antibody levels compared with other infantswho had not been given acetaminophen.

Another study in adults did not find their antibody levels fell after being vaccinated and taking acetaminophen. Immune responsescan differ between children and adults.

Evans said the ability to mount a strong immune response also tends to go down as we age.

"What's the difference between different age groups, different types of anti-inflammatory or antipyretics?" Evans said. "They're all likely to be important and we just don't know the answer."

In the absence of those answers, authorities such as the U.S. Centers for Disease Control and Prevention (CDC) and World Health Organization say the use of antipyretics or fever-reducing medications is not recommended before or at the time of vaccination. They are approved in the days after vaccination.

For COVID-19 vaccines, Canada's National Advisory Committee on Immunization (NACI) gives similar advice.

"NACI recommends that prophylactic oral analgesics or antipyretics (e.g., acetaminophen or ibuprofen) should not be routinely used before or at the time of vaccination, but their use is not a contraindication to vaccination," according to the Government of Canada's website. "Oral analgesics or antipyretics may be considered for the management of adverse events (e.g., pain or fever, respectively), if they occur after vaccination."

The side-effects of vaccination such as a sore arm at the site of injection or wider effects like headache, fatigue, fever, muscle and joint soreness, while uncomfortable, are generally mild.

Bright side of mild vaccine side-effects

"All those side-effects are like a bell ringer telling you that your body is ramping up immune response," Evans said. "It's what you want. It's sometimes disappointing if you didn't get that response."

If you do spike a fever after receiving the COVID-19 vaccination, Evans said the best advice is to stay home and ride it out.

If the temperature reaches 39.4 C or 103 F, redness or tenderness in the arm increases after a day or if side-effects don't go away after a few days, theCDC says call your doctor.

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Likewise, if you're regularly taking anti-inflammatory or pain and fever-relieving medications for a chronic condition, Evans suggests contacting your doctor about what to do about taking the medications around the time of COVID-19 vaccinations.

The CDC suggests holding a cool, wet washcloth over the area of the shot and exercising that arm. For fever, drink lots of fluids and dress lightly.