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FluMist Found Safe in Latest Study

Two years after intranasal vaccine's introduction to market, new evidence backs its use in healthy people

TUESDAY, Dec. 6, 2005 (HealthDay News) -- Two years after being introduced to the market, the FluMist intranasal vaccine appears to be safe for use among healthy people aged 5 to 49, according to the latest evidence.

"It sort of confirms in a very major way the overall safety of this vaccine for the age groups for which it has been specifically used," said Dr. Pascal James Imperato, chairman of the department of preventive medicine at State University of New York Downstate Medical Center, in New York City. "I don't think there's terribly much new here that we didn't know before, but it gives an added margin of comfort."

The findings appear in the Dec. 7 issue of the Journal of the American Medical Association.

Until the 2002-2003 flu season, the only licensed flu vaccine in the United States was the inactivated, trivalent injectable vaccine, better known as the annual flu shot.

In June 2003, the U.S. Food and Drug Administration licensed a trivalent live, attenuated influenza vaccine, which could be administered as a nasal spray to healthy individuals aged 5 to 49. Known as FluMist, it contains weakened influenza viruses. Unlike the flu shot, which contains completely inactivated flu viruses, FluMist carries the possibility that the virus will reproduce and cause disease, especially in people who are not in optimal health.

Given shortages in the supply of conventional flu vaccine in recent years, FluMist has been a welcome addition to the medical arsenal against influenza, which causes an estimated 36,000 deaths annually in the United States.

Last year, the United States experienced severe shortages in flu vaccine supply because of problems at the British manufacturing plant of one of the country's major flu vaccine suppliers. So far this year, officials are predicting adequate supplies, although specific areas have reported problems.

To help ensure that the most vulnerable people, such as the elderly and ill, get vaccinated, Dr. Julie Gerberding, director of the U.S. Centers for Disease Control and Prevention, has urged that healthy people between the ages of 5 and 49 use the nasal version of the vaccine.

Pre-licensure testing of Flu Mist involved 20,228 people, a large number but still not enough to detect rare adverse events.

Some 2.5 million people have since received FluMist during its first two seasons, 2003-2004 and 2004-2005. This large pool of people has given investigators a chance to see if additional, unexpected side effects might crop up.

The authors of this latest study, led by Dr. Hector S. Izurieta of the FDA, looked at the Vaccine Adverse Event Reporting System (VAERS), operated by the FDA and the CDC since 1990.

As of Aug. 16, the system had received and recorded 460 adverse event reports for FluMist vaccinations received from August 2003 through July 2005.

No fatalities were reported, although there were seven reports of possible anaphylaxis (a severe allergic reaction), two reports of Guillain-Barre syndrome (a temporary inflammation of the nerves), one report of Bell palsy (paralysis of the facial muscles), and eight reports of asthma exacerbation among individuals who had a prior history of asthma. It was not clear if all of these reactions were due to the vaccination.

Sixteen percent of these reports were in individuals for whom the vaccine was not indicated. FluMist is not recommended for individuals with asthma or other underlying conditions. VAERS is not helpful in evaluating adverse events in people for whom the vaccine is not indicated.

"It leaves open the question of the safety of this with regard to people who are immuno-compromised," Imperator confirmed.

A second study in the same issue of the journal found that hospitalization rates for pneumonia, one of the major complications of influenza, have increased substantially in elderly U.S. adults over the past 15 years.

The reason appears to be an increase in chronic underlying conditions such as heart disease, lung disease and diabetes, the authors reported.

"Having this information helps you get a sense of some of the important problems, and where we might direct our efforts," said study author Dr. Alicia Fry, a medical epidemiologist with the CDC. "We certainly think the elderly should continue to get vaccinated, but we also think there's room for exploring new vaccine development."

More information

Get the latest on the flu vaccine from the U.S. Centers for Disease Control and Prevention.

SOURCES: Pascal James Imperator, M.D., chairman, department of preventive medicine, State University of New York Downstate Medical Center, New York City; Alicia Fry, M.D., medical epidemiologist, U.S. Centers for Disease Control and Prevention, Atlanta; Dec. 7, 2005, Journal of the American Medical Association
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