By GARDINER HARRIS

Published: August 25, 2011

Yet another panel of scientists has found no evidence that a popular vaccine causes autism. But despite the scientists’ best efforts, their report is unlikely to have any impact on the frustrating debate about the safety of these crucial medicines.

“The M.M.R. vaccine doesn’t cause autism, and the evidence is overwhelming that it doesn’t,” Dr. Ellen Wright Clayton, the chairwoman of the panel, assembled by the Institute of Medicine, said in an interview. She was referring to a combination against measles, mumps and rubella that has long been a focus of concern from some parents’ groups.

The panel did conclude, however, that there are risks to getting the chickenpox vaccine that can arise years after vaccination. People who have had the vaccine can develop pneumonia, meningitis or hepatitis years later if the virus used in the vaccine reawakens because an unrelated health problem, like cancer, has compromised their immune systems.

The same problems are far more likely in patients who are infected naturally at some point in their lives with chickenpox, since varicella zoster, the virus that causes chickenpox, can live dormant in nerve cells for decades. Shingles, a painful eruption of skin blisters that usually affects the aged, is generally caused by this Lazarus-like ability of varicella zoster.

The government had asked the institute to review the known risks of vaccines to help guide decisions about compensation for those who claim to have been injured by vaccines. Legislation passed by Congress in 1986 largely absolved vaccine makers of the risks of being sued for vaccine injuries and forced those who suffer injury to petition the government for compensation.

The government generally restricts compensation to cases involving children who suffer injuries that scientists deem to have been plausibly caused by vaccination, including seizures, inflammation, fainting, allergic reactions and temporary joint pain. But battles have raged for years over whether to expand this list, with most of the fighting revolving around autism.

Many children injured by vaccination have an immune or metabolic problem that is simply made apparent by vaccines. “In some metabolically vulnerable children, receiving vaccines may be the largely nonspecific ‘last straw’ that leads these children to reveal their underlying” problems, the report stated.

For instance, recent studies have found that many of the children who suffered seizures and lifelong problems after receiving the whole-cell pertussis vaccine, which is no longer used but once routinely caused fevers in children, actually had Dravet syndrome, a severe form of epilepsy. The flood of lawsuits over the effects of the whole-cell pertussis vaccine was the reason Congress created the national vaccine injury compensation program in the first place, and children who suffered seizures after getting this vaccine have been among the most well-compensated.

In retrospect, the whole-cell pertussis vaccine may have played little role in the underlying illness in many of these children other than to serve as its first trigger.

The Institute of Medicine is the nation’s most esteemed and authoritative adviser on issues of health and medicine, and its reports can transform medical thinking around the world. The government has asked the medicine institute to assess the safety of vaccines a dozen times in the past 25 years, hoping the institute’s reputation would put to rest the concerns of some parents that vaccines cause a host of problems, including autism. It has not worked.

Sallie Bernard, president of SafeMinds, a group that contends there is a link between vaccines and autism, said the latest report from the Institute of Medicine excluded important research and found in many cases that not enough research had been done to answer important questions.

“I think this report says that the science is inadequate, and yet we’re giving more and more vaccines to our kids, and we really don’t know what their safety profile is,” Ms. Bernard said. “I think that’s alarming.”

Dr. Clayton said: “We looked at more than a thousand peer-reviewed articles, and we didn’t see many adverse effects caused by vaccines. That’s pretty remarkable.”

http://www.nytimes.com/2011/08/26/health/26vaccine.html?hpw