COVID Vaccine Side Effects May Come From Your Expectations—Not the Unexpected

key takeaways

  • Many of the side effects people reported in COVID-19 vaccine trials also occurred in people who were not vaccinated (placebo), a new study shows.
  • After the first and second doses of the vaccine, the findings were consistent.
  • Experts say the “nocebo” effect is common in vaccines in general, not just COVID vaccines.

Potential COVID-19 vaccine side effects have been a big concern for people nervous about getting vaccinated. However, new research has found that many of the side effects people report are actually just placebo effects.

How placebos work

The study was published in JAMA Network Open, analyzed 12 articles that included data on side effects reported by 45,380 COVID-19 vaccine trial participants. Some people in the trial got the actual COVID vaccine, while others got a placebo: a vaccine that looks the same but doesn’t have any actual COVID vaccine.

Systemic and local side effects

Systemic side effects are felt throughout the body (eg, muscle pain), not just in one area (eg, arm pain at the injection site).

The researchers found that 35 percent of those who received the placebo injection reported systemic side effects after taking the first dose. After the second dose of the vaccine, 32% of the placebo group reported systemic side effects.

The most common symptoms were headache (19.6%) and fatigue (16.7%).

COVID-19 vaccine expected to have mild side effects

However, those who get real The COVID vaccine reported more side effects than people who got a placebo. The researchers found that after the first dose of the real vaccine:

  • 46% reported at least one systemic side effect
  • 67% reported at least one “local” event (such as pain or swelling at the injection site)

After the second dose of vaccine:

  • 61% reported systemic side effects
  • 73% reported local side effects

placebo effect

However, some of these side effects also occurred in the placebo group. Since these people didn’t get the real COVID vaccine, that means their side effects didn’t happen as a result of the injection. If a person experiences side effects from a placebo treatment, it is called the placebo effect.

As a result, the researchers estimated that people in the placebo group accounted for 76 percent of reported side effects after the first dose and 52 percent of the reported side effects after the second dose.

Are the side effects of the COVID vaccine contagious?

The researchers used the term “nocebo” to describe what people who received a placebo experienced. The “nocebo effect” is when a person’s expectation of experiencing a negative event after treatment (for example, a vaccine side effect) makes them more likely to have a negative experience.

The researchers concluded that their study “found a high rate of nocebo responses in the placebo arm of the COVID-19 vaccine trial.”

COVID vaccine side effects

Potential side effects of the COVID-19 vaccine vary from person to person. Some people don’t have any side effects at all.

In general, the most common topical vaccine side effects include:

  • pain
  • redness
  • swelling

The most common systemic vaccine side effects include:

  • tired
  • headache
  • Muscle pain
  • chills
  • fever
  • nausea

Timeline of COVID-19 Vaccine Side Effects

The “nocebo effect” is common

The nocebo effect is common, Thomas Russo, MD, professor and head of infectious diseases at the University at Buffalo, told VigorTip. That’s why it’s so important for researchers to “run a control or placebo group” when they’re testing the efficacy of treatments like vaccines.

Amesh A. Adalja, MD

The placebo effect is a strong and real phenomenon.

— Amesh A. Adalja, MD

Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, told VigorTip that they were “not surprised” by the study’s results because “the placebo effect is a strong and real phenomenon,” And “vaccination by injection is a medical procedure, and even the use of a placebo can have an effect.”

The nocebo effect isn’t just happening in the COVID lens, Russo added. “In any trial, the placebo group had side effects,” “it’s how people react when they perceive something they’re receiving, not a true causal relationship to that thing.”

placebo effect

Why the Nocebo Effect Happens

Doctors say there are several potential reasons why the nocebo effect occurs. Richard Watkins, MD, an infectious disease physician and professor of internal medicine at Northeastern Ohio Medical University, told VigorTip that this is simply due to expectations.

Richard Watkins, MD

This suggests that vaccines are much safer than many believe.

— Richard Watkins, MD

“People are so used to it that if they get an injection, they’re going to have some kind of bad reaction,” Russo said, adding that others are just nervous about needles and may react based on that fear.

“Some people think their bodies have been invaded,” Russo said. “As a result, they may develop symptoms that are not related to the vaccine.”

Fear of COVID-19 outweighs fear of vaccine side effects

Experts stress that the study’s findings suggest that the side effects of the COVID vaccine itself are not as common as many people think.

“This shows that the vaccine is much safer than many people think,” Watkins said. “If you subtract the perception of injection-related side effects compared to the side effects caused by the vaccine itself, the actual number of side effects is much lower,” Russo said.

Adalja urged people who are nervous about getting a COVID vaccine to consider that “overall, the COVID-19 vaccine is very safe, and many of the reactions people may experience may not be related to the vaccine’s components.”

what does this mean to you

Like any vaccine, the COVID-19 vaccine can have side effects. However, recent research suggests that these side effects may not be as common as one might think.

If you are nervous about getting vaccinated because of concerns about side effects, share your concerns with your doctor. They can make sure you understand how vaccines work, why they are safe, and the risks and benefits of getting vaccinated.

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The information in this article is current as of the date listed, which means that you may have updated information as you read this article. For the latest updates on COVID-19, visit our Coronavirus news page.