The majority of side effects from the vaccine reported so far have been among women. This might be because women are more likely to willing than men to acknowledge symptoms like headache and fatigue, but there also may be a biological reason why women experience more severe side effects than men, experts say.
"We know that with vaccinations and infections, women tend to have a stronger immune response than men," Dr. Simone Wildes, a Boston-based infectious disease specialist, told "Good Morning America." "That’s really driven by biological differences in males and females and the sex hormones."
Stephanie Durocher, a middle school teacher in Raleigh, North Carolina, felt the difference firsthand when she received the Moderna vaccine last month.
After her first shot, Dorucher said she experienced a rash at the injection site, which she said also felt hot and itchy.
After her second shot last week, Dorucher was sidelined with side effects including body aches, fever, chills and nausea, which she described as "five days of horrible."
Those types of side effects are playing out for women across the country -- in the first 13.7 million COVID-19 vaccine doses given to Americans earlier this year, 79% of the reports of side effects were reported by women, according to the Centers for Disease Control and Prevention.
The most frequently reported symptoms were headache, dizziness and fatigue, according to the CDC.
Thankfully, vaccine side effects are temporary, usually going away within a day or two after the shot. And allergic reactions are exceedingly rare, happening in fewer than five people out of every 1 million shots given.
Wildes explained that women and men experience different side effects because the COVID-19 vaccine prompts the body to make foreign proteins, and women's bodies react differently than men's.
"When we get the COVID vaccine, we are introducing proteins into our body that are foreign and we’re teaching the cells to make the antibodies and the T-cells to help to fight the infection in case we’re exposed to it," she said. "What happens in the female body is those cells create more protein than the male cells would."
"When females get the vaccine, we’re going to complain of more side effects because our immune system is more revved up," Wildes explained. "We are able to produce more of the antibodies, the T-cells against this foreign material, the COVID-19 vaccine."
The different immune responses between men and women also could help explain why men have experienced a higher fatality rate of COVID-19 throughout the pandemic, according to Wildes.
Experts like Wildes say women's tendency to report medical symptoms more could also be a factor in the higher percentage of women reporting COVID vaccine side effects.
"Women in general just report more, so there is that difference," said Wildes. "I can’t tell you how many men I will see in the hospital who say, ‘My wife forced me to go to the hospital,' while some men will say, 'It's not a big deal.'"
The different reactions between men and women to the COVID-19 vaccine track with what experts have also seen with other vaccines, like the flu shot, according to Wildes.
She stressed that reports of side effects should not deter any women from getting vaccinated against COVID-19.
"We are seeing more side effects with women and that doesn’t mean they shouldn’t get it, it just means that's what we’re seeing," said Wildes. "Don’t let that be a gauge to say, 'Well maybe I shouldn’t get it.'"
"Being informed about what to expect really makes a difference," she added.
People who get a COVID-19 vaccine may feel pain, redness and swelling in the location of the shot, according to the CDC, adding that throughout the body people may feel fatigue, muscle pain, chills, fever, headaches and nausea.
According to the CDC, people should avoid taking painkillers like ibuprofen before getting a covid-19 vaccine shot because it's not clear if these medications will interfere with the vaccine's effectiveness. However, the CDC says it should be safe to take a painkiller after getting the shot, to treat any pain or discomfort, after discussing with your doctor.
Most people can expect the side effects to go away "within a few days." People should contact their health care provider if side effects are worrisome to them and/or do not go away after a few days, according to the CDC.
Wildes explained that any side effects are normal signs that the vaccine is working in your body. She also noted that the response has "no correlation to how the vaccine is working in your body."
"Each person’s response is different," said Wildes. "We’re telling you what to expect [with side effects] so you’re not alarmed and can be prepared for what comes."