Is the COVID-19 vaccine effective if you don’t have a reaction to it?

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Is the COVID-19 vaccine effective if you don’t experience a reaction after receiving it? 

The two coronavirus vaccines have seen emergency approval in the U.S. — one developed by Pfizer-BioNTech and the other by Moderna — may cause side effects after they’re administered, such as pain and swelling at the injection site, and/or fever, chills and headache, according to the Centers for Disease Control and Prevention (CDC). 

Since vaccination initiatives began, many patients have reported experiencing so-called "COVID arm" after receiving the jab, while others hoping to avoid any unpleasant side effects have been warned not to take over-the-counter pain relievers beforehand, as experts are concerned that doing so could impact the vaccines’ effectiveness. 

Even the nation’s nation’s top infectious disease expert, Dr. Anthony Fauci, said he was "knocked out" for about a day after receiving the second dose of the Moderna vaccine. 

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But what if you don’t have any reaction after receiving the jab — was it still effective? 

Yes, say various experts who spoke to Fox News. 

"The COVID vaccine is ‘reactogenic,’ which means they create an immune response that often causes side effects. The second dose typically results in more intense side effects because it is a boost. You have already primed your immune system so by the second one, you should develop a more robust immune response. This is not unusual — several vaccines are reactogenic — including shingles," explained Dr. John Whyte, the chief medical officer of the health care website WebMD. 

But don’t be alarmed if you feel just fine after receiving the jab, even after the second dose, he said. 

"If you don’t get any side effects or only very mild ones, don’t be alarmed. That does not mean your immune system is not working.  Everyone’s immune response is a little different and less than half of the people in the studies had any side effects." 

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"When it comes to vaccines (COVID-19 and others), the phrase, ‘No pain, no gain’ does not apply. Studies do not support the idea that if you have a mild reaction or no reaction you are less protected. The immune system is incredibly complex and everyone will react differently and for different reasons," said Dr. Shira Doron, an infectious disease physician and hospital epidemiologist at Tufts Medical Center, to Fox News. 

"Overall, younger people tend to react more vigorously, women have more local reactions (but not more generalized reactions), and the reactions after the second dose are more prominent than after the first," she added. "But," she noted, "your experience may be quite different."

Dr. Richard Ellison, meanwhile, said those who do not have any reactions following vaccination may just be "luckier." 

"Having symptoms means that your body is reacting to the vaccine but people can also have a very good antibody response without symptoms. They are just luckier," Ellison, an epidemiologist at UMass Memorial Medical Center, said. "It is also more common to have a reaction after the second dose, which is very typical after two-dose vaccines."

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For those who do experience vaccine side effects, the CDC advises placing a clean, cool, wet washcloth over the injection site should one experience pain, while also recommending to "use or exercise your arm" to reduce any discomfort. 

The federal agency also advises to "drink plenty of fluids" and "dress lightly" in the case of a fever. 

Those who experience an increase of redness or tenderness at the injection site 24 hours after receiving the vaccine, or have any "worrying" side effects that don’t subside after a few days should speak to their doctor, the CDC says.