Common childhood immunizations do not cause chronic diseases such as autism and diabetes, finds a new expert report that may ease parents' fears about the safety of vaccines.
Authors of the nearly 700-page report, released Thursday, say they took pains to carefully consider virtually every potential complication. While all drugs have side effects, the report notes that vaccine-related complications are extremely rare. Overall, vaccines' enormous benefits far outweigh the risks, says study co-author S. Claiborne Johnston of the University of California-San Diego.
"We're talking about millions of doses of vaccines, and only a few case reports of these rare events," Johnston says.
Some parents today are skipping or delaying their children's shots based on unfounded fears, says Austin pediatrician Ari Brown, a spokeswoman on vaccines for the American Academy of Pediatrics. She was not involved in the new report.
Parents, doctors or others can report possible vaccine side effects to a national database, called the Vaccine Adverse Event Reporting System. But there's little evidence that any of these problems are caused by vaccines, Brown says. In many cases, what seems like a side effect or allergic reaction is actually just a coincidence.
Many suspected side effects are so rare that doctors can't even estimate how vaccines might increase or decrease the risk of developing them, the report says.
Brown praised the report and the 12,000 peer-reviewed studies behind it. She notes that vaccines have been scrutinized more carefully than virtually any other medication. As a pediatrician, she says she's seen kids have allergic reactions to many medications, including the antibiotics that many parents demand during cold season.
Parents' refusal of vaccines is allowing once-forgotten diseases to re-emerge, says William Schaffner, an infectious disease expert at Vanderbilt University, who wasn't involved in the new report.
The Centers for Disease Control and Prevention has said that unvaccinated people are fueling the current measles epidemic, which has affected 193 people so far this year. That's more than three times the usual number of measles cases for an entire year.
"People forget what these diseases are like," says Ellen Clayton, chair of the committee and director of the Center for Biomedical Ethics and Society at Vanderbilt University in Nashville. "When I was a resident, we had a child in the hospital with tetanus. You don't want to see that happen."
Clayton says her committee wanted to make safety data easily available, so that parents can make informed decisions. The CDC also publishes a "Pink Book" with detailed vaccine information on its website.
The Institute of Medicine "reviewed all of the data as is humanly possible, and it's very reassuring," says Greg Poland, a professor of infectious disease at the Mayo Clinic in Rochester, Minn., who wasn't involved with the report. "Serious side effects are very, very rare."
Some of the most common side effects of vaccines are minor annoyances, such as sore arms or fainting, Johnston says.
Authors made a handful of definitive conclusions. In spite of rumors to the contrary, for example, evidence clearly shows that flu shots don't trigger asthma attacks or cause a type of facial paralysis called Bell's palsy. However, data do show that getting a combined measles-mumps-rubella shot can increase the risk of fever-related seizures in children, a frightening but benign condition that does no lasting harm. It occurs in 4% of children under age 5.
Yet getting the measles also increases the risk of these seizures, as well as many more serious problems, Schaffner says.
When serious side effects do occur, they're usually in children with known risks, such as immune deficiencies, Johnston says.
Vaccines still pose little threat to these kids, however, because pediatricians know not to give them certain shots, Schaffner says.
In many ways, vaccines today are far safer than in past generations, says Paul Offit, an infectious disease expert at Children's Hospital of Philadelphia, who wasn't involved in the new report. For example, the polio shots that children receive today are much safer than the liquid medicines given to their parents. Children today also get a whooping cough shot that's less likely to cause allergic reactions. And smallpox shots, which could in rare cases cause death, haven't been given for decades.
Poland says he hopes the report helps to ease parents' fears and help them put aside worries about vaccine safety. The Institute of Medicine has reviewed the issue 11 times in the past 25 years. While all of the authors have scientific backgrounds, none are vaccine researchers.