Experts say side effects are actually a good thing after the vaccine, so what if you feel fine?

By Amber Brenza
April 09, 2021
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I started preparing for my second dose of the Pfizer COVID-19 vaccine the day before I was set to get it. I got a full workout in, I made sure we had some Tylenol on hand, I bought chicken noodle soup and saltine crackers and ginger ale—all in an effort to make myself as comfortable as possible for any impending side effects from the vaccine.

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Credit: Getty Images

According to the Centers for Disease Control and Prevention, all three of the vaccines authorized for emergency use by the FDA—Pfizer-BioNTech, Moderna, and Johnson & Johnson—can cause any combination of the following symptoms:

  • Pain, swelling, or redness at the injection site
  • Fatigue or tiredness
  • Headache
  • Muscle pain
  • Fever and chills
  • Nausea

As a 32-year-old woman, the deck felt stacked against me even more: Research from the CDC published in February found that, of people who reported vaccine side effects, 79.1% were women—even though 61.2% of study participants vaccinated were women. And other data shows that young people experienced more local and systemic (whole body) side effects than those who are older. Data from all vaccine trials, published on the CDC's website, show that people ages 18 to 55 (or 59 or 64, depending on the specific vaccine) experienced local or systemic side effects more often than those over that age limit.

The tweets and 'grams didn't help either: It seemed everyone felt like they'd been hit by a train the day after their shot. I thought all the evidence was there—I completely expected to feel like garbage the day after my second dose, and I just had to be OK with that.

Except...I felt fine. No symptoms a few hours after the vaccine when I went to bed. No symptoms when I woke up at 3 a.m., a full 12 hours after my shot. No symptoms when I woke up the next morning.

Obviously, no one wants these side effects, but it felt strange that I didn't even feel a tinge of a headache or an urgent need for a nap. My mind circled back to those stories on COVID-19 vaccine side effects and how experts have told us that experiencing side effects can be a good sign that your body is building protection against the virus. "The bigger your body's immune response, the more likely you're going to feel like you have a flu-like illness," Kathleen Mullane, DO, PharmD, professor of medicine and director of infectious disease clinical trials at the University of Chicago, previously told Health.

So if I didn't feel any side effects from either of my COVID-19 vaccines, should I be worried that my body didn't mount enough of a response? Not really, according to Amesh A. Adalja, MD, senior scholar at Johns Hopkins Center for Health Security. "While it's true that vaccine side effects are often attributed to the vaccine 'taking' or prompting a reaction, if they are not experienced, it doesn't mean one is not sufficiently protected by the vaccine," he tells Health. "Each person's immune system has some idiosyncrasies that could be at play."

"Everyone is different," adds Richard Watkins, MD, infectious disease physician and professor of internal medicine at the Northeast Ohio Medical University. "So just because you have no symptoms after the vaccine doesn't mean there is a problem," he tells Health.

Though it's often overlooked, the evidence suggests this too. "In all of the vaccine studies, at least 20% of people felt nothing post-vaccination and most side effects were fairly insignificant, such as injection site pain," Lewis S. Nelson, MD, professor and chair of the Department of Emergency Medicine, and director of the Division of Medical Toxicology at Rutgers New Jersey Medical School, tells Health.

That goes for both clinical trials and real world situations (cough, me, cough). In the Pfizer vaccine trials, 77.4% of people reported at least one systemic reaction—that means nearly 1 out of every 4 patients didn't experience those side effects at all. Slightly more people felt systemic reactions after a second Moderna shot—81.9%—but that still means about 1 out of every 5 patients felt fine. The rates for Johnson & Johnson's vaccine were even better: Though reactions were broken up by age groups, only 45.3% of people over 60 years old felt any systemic side effects, while 61.5% of people ages 18 to 59 did.

And that's from the same data that found those vaccines to be effective at preventing not only severe disease in clinical trials, but also hospitalization and death from COVID-19.

It's good news for those of us who were anxious about not feeling like crap after the vaccine—even if we don't necessarily know why these differences in reactions happen. "Every person reacts differently to the vaccine, just like they do when exposed to COVID, and the response is somewhat unpredictable in any individual," says Dr. Nelson. And just because someone has a strong response to the vaccine doesn't necessarily mean they've acquired more protection—it just means they had more of an inflammatory response as their bodies crafted protective immunity, William Moss, MD, executive director of the International Vaccine Access Center at Johns Hopkins Bloomberg School of Public Health, tells Health. "People who don't have any side effects are just as likely to be protected as people who have severe side effects," he says.

The bottom line here: If you didn't feel any side effects after your COVID-19 vaccine, it's not something to worry about—you still have the same protection as someone who had to stay in bed the day after their jab.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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