Vaccine Side Effects Occur Rarely, Report Finds

Vaccine needle (Image credit: Dreamstime)

Reactions to vaccines are extremely rare, and most are easily treated, according to a new review of more than 1,000 vaccine studies.

Vaccines have rarely caused seizures, brain inflammation, and fainting, and have significantly reduced rates of death and disability, said the report from the Institute of Medicine (IOM).

The report was done to assess whether eight vaccines, including the measles-mumps-rubella (MMR), cause adverse health effects.

There is no evidence that vaccines cause autism, Type 1 diabetes, or exacerbate asthma, the report said. Some parents have been concerned about vaccinating their children because of suggestions that the shots may cause these problems, the researchers said.

"The findings should be reassuring to parents that few health problems are clearly connected to immunizations, and these effects occur relatively rarely," said Dr. Ellen Wright Clayton, a professor of pediatrics at Vanderbilt University in Nashville, and member of the IOM committee that put together the report." With the start of the new school year, it's time to ensure that children are up to date on their immunizations , making this report's findings about the safety of these eight vaccines particularly timely."

The report adds to the numerous studies refuting the link between autism and the MMR vaccine . The link was first proposed by a 1998 paper that has since been widely discredited and shown to be fraudulent. [See Beyond Vaccines: 5 Things that Might Really Cause Autism ].

"We have a lot of evidence that vaccine saves lives and averts a lot of suffering," Clayton said in a news conference about the report today. "The side effects that we're talking about here are really relatively rare. And the majority of the ones that we found are actually either short-term or readily treated."

Vaccine safety

The Institute of Medicine is required by Congress to periodically review the scientific evidence linking vaccines with health risks. This is the first report on adverse effects from vaccines since 1994.

The committee reviewed population studies, clinical studies and reports of individual adverse reactions.

The vaccines included were the MMR, flu, chickenpox, hepatitis B, human papillomavirus (HPV), hepatitis A, and meningococcal vaccines, and tetanus-containing vaccines.

The report found convincing evidence that 14 adverse health outcomes can be caused by these vaccines. These problems include:

  • Fever-triggered seizures in children caused by the MMR vaccine. These events are rare. Studies show between 3,000 and 4,000 children need to be vaccinated to have one extra case of fever-triggered seizure. These seizures almost always do not cause harm over the long term, the researchers said.
  • Brain swelling, pneumonia, hepatitis, meningitis, shingles, and chicken pox in those who receive the chicken pox vaccine. Most of these problems are found in people with compromised immune systems.
  • Anaphylaxis, an allergic reaction that happens after injection, was linked to the MMR, chicken pox, influenza, hepatitis B, meningococcal, and tetanus-containing vaccines.

Evidence of the more serious reactions, such as brain inflammation and anaphylaxis, was only found in reports of individual cases, said Dr. S. Claiborne Johnston, of the University of California, San Francisco, who was also on the committee. The fact that these reactions don't show up in studies of populations suggests that they are rare, Johnston said.

In many cases, there was too little evidence to say whether vaccines did or did not cause a specific health problem, the researchers said. There were more than 100 adverse reactions that fell into this category, Clayton said. An example is whether the flu vaccine causes Guillain-Barre syndrome. "In other words, we just don't know," whether vaccines cause these events, Clayton said.

Taking risks

Concerns over vaccines have led some people to choose to forego immunization, either for themselves or their children. "When you get an erosion in trust in start to see outbreaks," such as the outbreaks of measles and whooping cough we have seen in recent years, said Dr. Paul Offit, chief of the Division of Infectious Diseases and the director of the Vaccine Education Center at the Children's Hospital of Philadelphia, who did not contribute to the report.

The new report will likely not sway those who believe vaccines are a government or drug company conspiracy, Offit said. But it might convince those who are unsure.

"For some, who I guess may still be on the fence, this provides yet another piece of reassuring evidence," about the safety of vaccines, Offit said.

Offit said that people who don't get vaccinated are still taking a risk they will be susceptible to whatever disease the vaccine helps prevent.

"The choice not to get a vaccine is not a risk-free choice," Offit said. "It's just a choice to take another risk."

Pass it on: Vaccines rarely cause adverse reactions.

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Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.