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COVID-19: Side Effects Are More Likely After Second Pfizer Or Moderna Dose; Here's Why

Feeling a bit sleepy, sore, and achy after getting your COVID-19 vaccine? Don't fret.
Feeling a bit sleepy, sore, and achy after getting your COVID-19 vaccine? Don't fret. Photo Credit: flickr/New York Governor's Office

Feeling a bit sleepy, sore, and achy after getting your COVID-19 vaccine?

Don't fret. Side effects are a sign that the body's immune system is responding to the dose, and that it's working, according to medical experts. 

One of them, Dr.Allison Arwady, the Chicago Department of Public Health Commissioner, said younger people are more likely to experience side effects because they "have more robust immune system broadly," according to a report by NBC 5 Chicago.

Women are also more likely to report side effects than men, Arwady said, noting estrogen can elevate immune responses, and testosterone can decrease it.

Side effects are more likely after the Pfizer or Moderna second shot because the immune response to the second shot is even stronger than the response to the first shot, Dr. Robert Wachter, chief of medicine at the University of California San Francisco told KGO-TV/ABC 7 in San Francisco.

Many of these side effects could last two to three days, Wachter said.

According to the Centers for Disease Control & Prevention (CDC), possible side effects on the arm in which a dose is given are:

  • Pain
  • Redness
  • Swelling

Possible side effects throughout the rest of your body, according to the CDC, are:

  • Tiredness
  • Headache
  • Muscle pain
  • Chills
  • Fever
  • Nausea

"The way I think about them (side effects) is it is a sign that it's working," Wachter told KGO-TV. "What is a little funky about that of course as soon as you say that people say 'Oh I didn't have side effects. Does that mean it's not working?' The answer is: no.

"These two things turn out to be true. The side effects are a sign that your body is producing its immune response. Not having side effects, you should consider yourself lucky, but the vaccine seems to work as well in people who didn't have side effects."

To reduce pain and discomfort where you get the shot, the CDC recommends vaccine recipients apply a clean, cool, wet washcloth over the area and use or exercise their arm.

Side effects after your second shot may be more intense than the ones you experienced after your first shot, according to the CDC. 

"These side effects are normal signs that your body is building protection and should go away within a few days," according to the CDC.

The Pfizer-BioNTech and Moderna vaccines both need two shots in order to get the most protection. 

"You should get the second shot even if you have side effects after the first shot, unless a vaccination provider or your doctor tells you not to get it," said the CDC.

People are considered fully vaccinated two weeks after their second shot of the Pfizer or Moderna vaccine, or two weeks after the single-dose Johnson & Johnson/Janssen COVID-19 vaccine. 

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