We Found Out Why Some People Won't Experience Any COVID-19 Vaccine Side Effects

Zee Krstic
·5 min read
  • Clinical trials suggest that most vaccinated individuals will not experience side effects after their first shot, with more experiencing no side effects at any point.

  • Your immune system is working against COVID-19 even if you do not exhibit any symptoms. 

  • Experts say two demographics may be more likely to experience no vaccine side effects, and not to be alarmed if your vaccine doesn't impact what's known as reactogenicity.

In preparing Americans to receive a vaccine, there has been plenty of talk about potential side effects associated with a COVID-19 vaccine. Most commonly, people have experienced one or a combo of temporary symptoms like fatigue, body pains and aches, chills, a slight fever or just a very sore, tender arm. And experts have also spotlighted increasingly rare reactions to the COVID-19 vaccine, like a delayed rash at the injection site that's being referred to as "COVID arm" in clinical research. National healthcare officials are taking each and every report of adverse side effects seriously — a major reason why the single-dose Johnson & Johnson vaccine is currently on pause following 6 incidents of extremely rare blood clotting.

With all this talk of side effects, you may be building up expectations in your head to be bedridden for a few days after your first or second dose. What does it mean, then, if your shot is largely uneventful? No, nothing is wrong with you — or the dose you've received, regardless of who has manufactured it. Many fail to realize that vaccine side effects are actually scientifically rarer than they are common; after all, during accelerated clinical Pfizer vaccine trials in 2020, more than 50% of participants didn't experience any side effects after being vaccinated, according to data highlighted by the New York Times.

And to be clear, the most common side effect currently is understood to be temporary arm pain, according to newly released research that pulled data from the Centers for Disease Control and Prevention's V-Safe system, which helps patients report any adverse reactions to a COVID-19 vaccine. This JAMA Insights report illustrates that most people weren't likely to experience significant reactions in general, especially not after the first dose. Arm pain, headaches and chills were more common after the second dose, but only in a minority of patients.

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At any rate, a lack of a physical reaction (caused by what's known as your body's "reactogenicity") to the COVID-19 vaccine doesn't mean your body isn't working on building immunity to the disease, explains Stanley Martin, M.D., an infectious disease clinician at Geisinger, a Pennsylvania-based healthcare system.

"Lots of vaccines work in different ways, but they are all stimulating your immune system to one degree or another; if you look at reactogenicity and those side effects, they vary a bit depending on the vaccine," he tells Good Housekeeping. "There's not necessarily any correlation between the reactogenicity side effects you experience and the success of your vaccine taking hold." 

Who is more likely to experience no vaccine side effects?

Everyone's immunity is different, so it can be true that two similar individuals — whether it be age, sex, current health status — experience vastly different side effects after vaccination... or none at all. But clinical trials on the vaccines in use in the United States suggested that certain demographics may be more likely to experience reactogenicity side effects, issues like fatigue or headaches, while others are less likely overall.

Older individuals have historically reported fewer side effects when it comes to COVID-19 vaccines, Dr. Martin points out. The younger you are, the more likely it may be that your immune response includes noticeable side effects, Dr. Martin explains. CDC officials noted in clinical trials that side effects were higher for those under the age of 55; data suggested, at the time, that younger people would experience more side effects than those who were older, especially after the second dose.

Women are more likely to experience noticeable vaccine side effects than men, per CDC data. Out of nearly 7,000 reports of side effects in early January, 80% were filed by women, most often citing headaches, dizziness or fatigue. Furthermore, teams behind the Moderna mRNA vaccine have shared that 77% of its reported side effects have come from women as well, according to USA Today.

Why do some people have no side effects?

It's a question that healthcare providers can't answer just yet. "There isn't one specific reason, per se; it's a multifactorial issue, where age and gender are just two small factors associated with the dilemma," Dr. Martin says. "There's a lot of other things that have to do with the way the immune system works: If you're someone who historically tends to experience side effects with vaccines, then you may be someone who's likely to experience side effects with COVID-19 vaccines as well."

Vaccine trials for both Pfizer and Moderna products suggested that a significant amount of people didn't experience side effects at one point or another, and yet, it proved to be 95% effective at preventing serious COVID-19 illness for all involved. Whether or not you've experienced one or four or six side effects during your vaccination process doesn't mean you're less or more protected than those who experienced none.

"There's a big chunk of people who aren't having those reactogenicity-produced side effects, but who are clearly being protected from these vaccines," adds Dr. Martin. Rest assured that you haven't done anything wrong; your immune system is working even if you don't experience side effects.

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