After reviewing more than 1,000 studies on the subject, a panel of experts from the Institute of Medicine released a report Thursday stating vaccines cause very few side effects. They also did not find evidence of a link between vaccines and autism or Type 1 diabetes.
The review is the most comprehensive on the subject in 17 years. The authors of the report write that it is not intended to answer the question of whether vaccines are safe, but to help quantify the risk of specific adverse events so that "other bodies," such as government agencies and care providers, can better weigh the risks and benefits.
The question of whether vaccines cause potentially dangerous side effects is an old one. One concern is that an immunization will give children the very disease it is meant to protect them from -- a common fear for flu vaccines -- or that it will cause a separate disease, such as autism. Critics are simply not 100 percent certain vaccines are safe.
The authors of the exhaustive new report say they made use of the best evidence currently available. Eight vaccines were examined: the human papillomavirus (HPV) vaccine, vaccines that contain tetanus, the hepatitis B vaccine, the measles-mumps-rubella (MMR) vaccine, the varicella vaccine for chickenpox, the influenza vaccine, the meningococcal vaccine and the diphtheria-tetanus-acellular pertussis (DTaP) vaccine.
Experts on the panel looked at the research to see whether it "convincingly supports," "favors acceptance" or "favors rejection" of a causal effect between vaccines and diseases and side effects. They found that the MMR vaccine was not linked with autism, and that the DTaP vaccine was not linked with Type 1 diabetes. In addition, the panel found that the flu vaccine was not linked with Bell's palsy or worsened asthma.
However, the panel did find some side effects associated with the vaccines, particularly among people with immune system problems. For example, the MMR vaccine was linked with seizures, as well as brain inflammation in immunocompromised people. Some of the vaccines were also identified as triggers for the allergic reaction anaphylaxis.
Barbara Loe Fisher, co-founder and president of the nonprofit National Vaccine Information Center, told The Huffington Post the most important takeaway of the new report is that there's still inadequate evidence in scientific literature "either way" in terms of causation. She dismissed the characterization of her group as anti-vaccine, saying that it is pro-education and pro-informed consent.
"The researcher priorities in this country are such that there is very little going on in vaccine safety science," Fisher told HuffPost. "In the meantime, doctors need to become partners with parents in informed consent. This push for oppressive one-size fits-all mandates from pharma and from organizations is not helping the situation. We need to make sure we're not bullied."
Perhaps the most hot-button vaccine included in the report is the MMR vaccine, which some parents and providers are concerned is linked with autism. The idea was first raised in a 1998 Lancet study by Andrew Wakefield, a British doctor who has since been stripped of his medical license. The study was called an "elaborate fraud" earlier this year in an investigation published in the British Medical Journal. But many parents still fear the potential of a link between the MMR vaccine and autism.
The federal Interagency Autism Coordinating Committee (IACC) is currently investigating a link between environmental factors and autism, including autism as a clinical outcome of vaccination.
The agency acknowledges that no epidemiological studies -- which involve tracking associations between the disease and people who have received vaccinations -- have so far shown a relationship between autism and thimerosal-containing vaccines. However, it said that these studies are "limited in their ability" to detect small groups of people who could be genetically more vulnerable to environmental factors for autism. The agency also said it would monitor any research exploring links between vaccines and autism.
The new Institute of Medicine report also examined potential side effects of flu shots. It specifically looked at whether the flu vaccine caused Bell's palsy, a paralysis of the facial nerve, or exacerbated asthma. The report found no association.
Many consumers harbor fears that the flu vaccine, which contains deactivated flu virus, could cause flu-like symptoms. A recent Consumer Reports study shows only about half of pregnant women got a flu shot during the last flu season. Women who chose not to get the shot feared risks to the baby and were afraid getting the vaccine would result in contracting the flu, according to Consumer Reports.
Some doctors also question the safety of the flu vaccine. Mark Hyman, M.D., an internationally recognized authority in the field of functional medicine, conducted and published on The Huffington Post a round-up of the evidence, concluding there is not enough scientific proof that flu vaccines actually work.
The official government stance from the U.S. Department of Health and Human Services is that everyone who is eligible should get a flu shot because vaccines are the best way to protect against the flu and keep the disease from spreading, a concept known as "community immunity."
And most doctors and health agencies are still strong proponents of childhood vaccinations. Some doctors are even turning away patients who choose not to follow the childhood immunization schedule, ABC News reported.
"[The] committee members spent an enormous amount of time reading thousands of articles," the Institute of Medicine report states. "Some of the conclusions were easy to reach ... some conclusions required substantial discussion and debate. Inevitably, there are elements of expert clinical and scientific judgment involved."
Catherine Pearson contributed reporting.