A high-powered scientific committee that examined the possible connection between vaccines and health problems found convincing evidence that some vaccines can cause rare adverse events in certain people, including seizures, brain inflammation and fainting.
The committee also found the evidence doesn't support any connection between autism and the MMR vaccine for mumps, measles and rubella (German measles).
In most cases, the committee said, there was insufficient evidence to reach any conclusion about connections between vaccines and dozens of other serious conditions. The 647-page report, "Adverse Effects of Vaccines: Evidence and Causality," was released Thursday.
The committee analyzed more than 1,000 research reports to reach its conclusion that 14 medical conditions can be linked to vaccines in rare cases.
It noted that many of these conditions are very unusual in the general population and most often occur without being preceded by vaccination.
The committee said figuring out the exact rate of adverse health events related to vaccines was not part of its charge.
The report uses cautious and scientific language, the committee said, because it is not possible to prove a negative -- to say, for example, that a vaccine did not and could not cause the particular condition. "We cannot say that in a certain person at a certain time, some event cannot happen; there is much about biology that is not known."
The vaccine that racked up the highest number of problems was the varicella vaccine, given to prevent chickenpox. In some patients -- most of whom had compromised immune systems -- the vaccine caused brain swelling, pneumonia, hepatitis, meningitis, shingles and chickenpox itself.
There was also convincing evidence, the committee said, that the MMR vaccine led to fever-triggered seizures for some children, although those seizures rarely had long-term consequences. However, for those with severe immune system deficiencies, the vaccine sometimes triggered a rare form of brain inflammation.
Both the varicella and MMR vaccines contain crippled live viruses.
Public health officials noted that the risks of particular vaccines to people with compromised immune systems are already known, and health organizations recommend against vaccination for those individuals.
Dr. Jeff Duchin, chief of communicable-disease control for public health for Seattle and King County, said the report's message was reassuring. "The conditions for which they found evidence are, by and large, conditions for which we were already aware" and precautions are in place, he said.
Clearly, Duchin said, the benefits of vaccines vastly outweigh the potential adverse events. Even now, there are cases of serious complications or death from vaccine-preventable diseases, he noted.
He praised the committee's suggestions that electronic medical records be used to gather better data in the future. "Overall, it's a good thing to have people continually scrutinize vaccines -- all of our treatments in medicine -- to make sure they're as safe as possible."
The 16 experts who made up the committee were convened by the Institute of Medicine, which was established under the charter of the National Academy of Sciences to provide independent, objective, evidence-based advice to policymakers, health professionals, the private sector and the public. The committee members included pediatricians, biostatisticians, and medical doctors and researchers in several fields, including immunology and neurology.
The report isn't likely to assuage vaccine critics, such as Bainbridge Island's Michael Belkin.
From Belkin's point of view, the IOM has an extreme pro-vaccine bias. So when that organization can't prove a vaccine doesn't cause a potentially dangerous health problem, he said, that should be "a red flag to anyone who is getting a vaccine shoved down their veins by a doctor or school that insists that vaccines are perfectly safe."
The committee acknowledged that some readers may be unhappy that the report doesn't appear to answer the question: Are vaccines safe?
"The committee was not charged with answering that question," it wrote. Other bodies make that determination, it said, including government agencies, care providers and industry, "as they determine the benefits and risks of marketing a product."
Vaccine policy, the committee said, "requires a balancing of risks and benefits."
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