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COVID-19 vaccines from Pfizer-BioNTech and Moderna are being offered to an increasing number of people. Vaccine recipients typically experience minimal side effects -- the most common being temporary pain and swelling at the injection site, fevers, chills, tiredness, muscle aches and pains and headaches.

While these side effects are generally a minor nuisance to most people, some attempt to prevent them by taking common over-the-counter pain relievers like acetaminophen (Tylenol) or ibuprofen (e.g., Motrin, Advil) beforehand. However, experts said these medications might not just dull the pain, but they may dull the vaccine from fully working.

"We do not recommend premedication with ibuprofen or Tylenol before COVID-19 vaccines due to the lack of data on how it impacts the vaccine-induced antibody responses," Dr. Simone Wildes, an infectious disease specialist at South Shore Medical Center and a member of Massachusetts' COVID-19 Vaccine Advisory Group, told ABC News.

The side effects from the vaccines are caused by activation of the immune system, meaning that the immune system is working and starting to build immunity to COVID-19 -- this is what we want. These pain relievers may prevent parts of the immune system from working and slow down the immune response. There is a theory that taking these medications before immunization may reduce their effectiveness.

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With flu season in full swing and the threat of H1N1 looming, demand for vaccines is at an all-time high. Although those vaccines are expected to be effective, University of Missouri researchers have found further evidence that some over-the-counter drugs, such as aspirin and Tylenol, that inhibit certain enzymes could impact the effectiveness of vaccines.

"If you're taking aspirin regularly, which many people do for cardiovascular treatment, or acetaminophen (Tylenol) for pain and fever and get a flu shot, there is a good chance that you won't have a good antibody response," said Charles Brown, associate professor of veterinary pathobiology in the MU College of Veterinary Medicine. "These drugs block the enzyme COX-1, which works in tissues throughout the body. We have found that if you block COX-1, you might be decreasing the amount of antibodies your body is producing, and you need high amounts of antibodies to be protected."

COX enzymes play important roles in the regulation of the immune system. The role of these enzymes is not yet understood completely, and medications that inhibit them may have adverse side effects. Recent research has discovered that drugs that inhibit COX enzymes, such as COX-2, have an impact on the effectiveness of vaccines. Brown's research indicates that inhibiting COX-1, which is present in tissues throughout the body, such as the brain or kidneys, could also impact vaccines' effectiveness.