Vaccines are generally safe for most people, the National Academy of Sciences has concluded, dismissing stubborn concerns about supposed links to autism and other serious health problems.
In the academy’s first comprehensive review of vaccine safety in 17 years, a committee of experts formed by the Institute of Medicine analyzed more than 1,000 research studies. They concluded that benefits outweigh the risks, which are rare and usually not life-threatening.
In a 667-page report released Thursday, the 16-member committee found convincing evidence that vaccines can cause 14 health problems, including seizures, brain inflammation, rashes and fainting, but said those complications appeared to be very uncommon. The committee also concluded there was evidence that some vaccines could cause other complications, such as allergic reactions and temporary joint pain.
But the committee found no link between being immunized and the most serious health problems that have raised concern, including autism and Type 1 diabetes.
“We have a lot of evidence that vaccines save lives and avert a lot of suffering,” said Ellen Wright Clayton, a professor of pediatrics and law at Vanderbilt University who chaired the committee. “The side effects we’re talking about here are really relatively rare . . . and the majority of the ones we found are either short-term or easily treated. That would be the take-home message.”
The safety of vaccines has become the subject of intense debate in the United States and elsewhere in recent years. Some parents have expressed concern that the rising number of inoculations recommended for children might be causing complications, leading some to refuse to get their children vaccinated against diseases such as measles, mumps and whooping cough.
Many public health authorities, however, have become increasingly alarmed that the refusals have led to a resurgence of infectious diseases that were once common killers but had been largely eliminated through wide-scale vaccination. In fact, a large outbreak of measles occurred in Europe this year, and the number of cases being reported in the United States this year has surged. This week, Maryland and Virginia health officials warned passengers who took an Amtrak train from Boston to Virginia last week that they may have been exposed to measles from an infected passenger. California has reported a resurgence of whooping cough.
Many prominent medical groups have repeatedly concluded that the benefits of vaccines outweigh the risks, and the purported link between autism and childhood vaccines has been uniformly disputed by leading authorities. But the new report is the most comprehensive look at the subject by one of the most prestigious scientific organizations. Vaccine proponents hoped that it would encourage more parents to get their children vaccinated.
“Although vaccines can cause certain problems rarely, on balance they are remarkably safe,” said Paul A. Offit, chief of infectious diseases at Children’s Hospital of Philadelphia.
The committee reviewed the existing scientific evidence for every commonly used vaccine and the complications possibly associated with each. It determined whether the studies showed that each vaccine clearly caused each possible complication, may have caused each complication, clearly did not cause any complications or whether there was insufficient evidence to know one way or the other.
Clayton acknowledged that there were more than 100 conditions for which the scientific evidence was inadequate to make a clear determination. The experts also could not quantify exactly how frequently side effects occur. That prompted critics of vaccines to question the report’s conclusions.
“The committee’s clear acknowledgment that there is a lack of adequate scientific understanding about the way that vaccines act in the human body, including how, when, why and for whom they are harmful, is confirmation that more and higher quality vaccine safety science is urgently needed,” Barbara Loe Fisher of the National Vaccine Information Center said by e-mail.
The Institute of Medicine has reviewed the safety of vaccines 11 times at the request of Congress since it enacted the National Childhood Vaccine Injury Act in 1986, with the last review occurring in 1994. The Department of Health and Human Services uses the reviews to administer the Vaccine Injury Compensation Program, which compensates the families of children injured by vaccines.
The committee concluded that there was convincing evidence that the measles-mumps-rubella (MMR) vaccine can lead to seizures triggered by fevers in some people. But that complication was almost always short-lived and did not lead to serious complications, the experts determined. The MMR vaccine can also cause a rare form of brain inflammation in some people with severe immune-system problems, the panel said.
“We looked very hard, and we did not find many adverse effects,” Clayton said. “I think that’s really good news.”
In a minority of patients, the chickenpox vaccine can cause brain swelling, pneumonia, hepatitis, meningitis, shingles or chickenpox, the committee found. But most of those cases occurred in people with immune system problems, according to analysis.
The MMR, chickenpox, flu, hepatitis B, tetanus and meningococcal vaccines can all cause an allergic reaction known as anaphylaxis shortly after getting the injections, as well as fainting and inflammation, the committee said. There is also weaker evidence that the vaccine can cause short-term joint pain in some women and children, according to the study, and some people can experience anaphylaxis after getting vaccinated against the human papillomavirus (HPV).
But the flu shot does not cause Bell’s palsy or worsen asthma, as had been feared, the committee concluded.
And while many studies have examined whether flu shots can cause Guillain-Barre syndrome, a neurological disorder, the committee was unable to say with certainty whether there was or was not a cause-and-effect relationship.
While it is impossible to prove there is no link between vaccines and autism, Clayton said, the weight of the evidence appears convincing.
“There have been a number of very strong studies looking at a large number of people. They consistently show no risk” for autism from the MMR vaccine, Clayton said.
The report’s release coincided with new federal data that showed that only about half of U.S. teenage girls had gotten vaccinated against HPV, a sexually transmitted virus that can cause cervical cancer. The vaccine has been dogged by concerns about safety and fears that the vaccine might encourage sexual activity. But Melinda Wharton of the Centers for Disease Control and Prevention said studies show that the vaccine is highly effective and safe.
“We’re talking about preventing cervical cancer,” Wharton said. “Not as many of our nation’s girls are receiving this life-saving vaccine as they should.”