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U.S. Panel Probes Safety of Flu Vaccine

Mar 14, 2003
By Todd Zwillich
Reuters Health

A government-sponsored panel of experts held its final public deliberations this week in preparation for an upcoming report detailing the safety of the nation's most widely used vaccine.

Experts from the Institute of Medicine will report sometime this summer on the scientific evidence surrounding the influenza vaccine, amid evidence that it can, in rare cases, cause severe reactions including a debilitating neurological disorder.

Approximately 80 million doses of flu vaccine were distributed in the 2002-2003 flu season, making it the most common form of immunization in the U.S.

The Advisory Committee on Immunization Practices at the U.S. Centers for Disease Control and Prevention (CDC) recommends flu vaccines for all adults over age 50, patients in nursing homes or other facilities, many children between 6 months and 18 years old, and other individuals who may be at risk.

Growing safety concerns among consumers over immunizations in general have also focused on the flu vaccine, which has been linked to several cases of Guillain-Barr Syndrome.

The CDC recorded approximately 70 cases of Guillain-Barr in vaccinated people in 1996-1997, though scientists believe that many more cases could have actually occurred. Cases have dropped steadily since 1997, and 15 were reported during last winter's flu season.

The agency now estimates that Guillain-Barr affects one to two persons for every million vaccinated, Dr. Robert T. Chen, head of the CDC's immunization safety branch, told the IOM committee.

But researchers still do not know how many of the cases are directly linked to the vaccine or how it might cause neurological problems.

"Parents are asking me all the time, 'What should I do?' '' said Dr. Lawrence Palevksy, a pediatrician based in Reston, Virginia. "The questions keep mounting and the answers aren't there," he said.

Bacterial contamination from eggs, which are used to manufacture the vaccine, was though to be the source of an outbreak in the 1976-1977 flu season in which 581 Guillain-Barr cases were diagnosed in people immunized against swine flu.

People were sickened by flu vaccines made by all four manufacturers who produced them at the time. Smaller Guillain-Barr outbreaks have occurred since even without apparent contamination, much to the confusion of scientists.

Dr. Chen told the committee that researchers suspect genetic differences may play a large role in determining who is vulnerable to the disorder following vaccination. "We have this one year [1976] that sort of sticks out like a sore thumb,' responded Dr. Christopher Wilson a member of the panel who is also a professor of immunology at the University of Washington.

Another study looking at a possible link between the flu vaccine and an increased risk of multiple sclerosis failed to produce a reliable connection, according to CDC researcher Dr. Frank DeStefano.

Causes of the flu vaccine's side effects are more difficult to determine than those of other vaccines in part because the vaccine's components change every year. Manufacturers constantly alter the viral contents of the vaccine to keep up with shifting strains of flu viruses as they travel the world.

Deciding what to do about potential side effects is also complicated by the fact that just one company-Aventis-Pasteur, currently manufactures the vaccine in the United States. Some witnesses warned that an IOM report that paints the flu vaccine as risky could jeopardize a domestic supply of the product.

"Please don't frighten the manufacturer away from manufacturing vaccine," said Dr. Robert G. Webster, professor of virology at St. Jude's Children's Research Hospital in Memphis, Tennessee. Dr. Webster told the committee that deciding whether or not to get immunized against the flu should be "a no-brainer" for most people since its benefits outweigh its risks.

While Guillain-Barr remains relatively rare, influenza is responsible for approximately 20,000 deaths and 115,000 hospitalizations in the U.S. each year, according to CDC figures.

The committee is expected to issue its report sometime in the next 3 months, said Dr. Marie C. McCormick, the panel's chair. The report will be the last in a series of immunization safety reviews that began in 2001.

© 2003 Reuters Ltd