After a close review of more than 1,000 research studies, a federal panel of experts has concluded that vaccines cause very few side effects, and found no evidence that vaccines cause autism or type 1 diabetes.
The report, issued on Thursday by the Institute of Medicine, part of the National Academies of Sciences, is the first comprehensive report on vaccine side effects since 1994.
Fears that vaccines might cause autism or other health problems have led some parents to skip vaccinating their children, despite repeated reassurances from health authorities. The concerns have also forced costly reformulations of many vaccines.
"We looked at more than 1,000 articles evaluating the epidemiological and biological evidence about whether vaccines cause side effects," said committee chair Ellen Wright Clayton, professor of pediatrics and law, and director of the Center for Biomedical Ethics and Society at Vanderbilt University in Nashville.
"The big take-home message is that we found only a few cases in which vaccines can cause adverse side effects, and the vast majority of those are short-term and self-limiting," she said in a telephone interview.
The report was commissioned by the U.S. Department of Health and Human Services to help guide the Vaccine Injury Compensation Program, which provides a pool of money to take care of children who experience side effects from vaccines.
The panel looked at eight common vaccines: the combination measles-mumps-rubella (MMR), the diphtheria-tetanus-acellular pertussis (DTaP), varicella for chickenpox, influenza, hepatitis B, meningococcal, tetanus-containing vaccines, and the human papillomavirus (HPV) vaccine.
SIDE EFFECTS ARE GENERALLY MILD
Once again, the IOM found that the MMR vaccine does not cause autism, nor does it cause type 1 diabetes, Clayton said.
"The DTaP vaccine, which is the pertussis vaccine, does not cause type 1 diabetes, and the killed flu vaccine does not cause Bell's palsy (temporary facial paralysis) and it doesn't make your asthma get worse," Clayton said.
"The evidence was really quite strong that vaccines don't cause these side effects," she said.
Among the side effects vaccines can cause, Clayton said most are short-lived. The panel found that the MMR vaccine can cause seizures in people who develop high fevers after getting the vaccine, but these pass quickly.
"They are scary to be sure, but they do not cause any long-term harm and they are not a sign the child will get epilepsy," Clayton said.
MMR can also cause a rare form of brain inflammation in some people with severe immune system deficiencies.
With the varicella vaccine against chickenpox, some people can develop brain swelling, pneumonia, hepatitis, meningitis or shingles, but this occurs most often in people with compromised immune systems.
Six vaccines -- MMR, varicella, influenza, hepatitis B, meningococcal, and the tetanus-containing vaccines -- also can trigger anaphylaxis, an allergic reaction that appears shortly after injection.
But Clayton said this can be addressed with the requirement by doctors to have patients remain in the waiting room for 15 minutes after their shot to make sure they do not have an allergic reaction.
She said the report should help people who are seeking to file claims for vaccine side effects, but it should also reassure many people that vaccines are largely safe.
"Despite looking very hard, it was really hard to find that vaccines cause injuries and the injuries they do cause are generally pretty mild and self-contained," she said.