updated 12/13/2006 5:03:04 PM ET 2006-12-13T22:03:04

The first head-to-head comparison of the flu shot and the new FluMist inhalable vaccine found shots surprisingly more effective in adults.

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The study, involving about 1,250 Michigan adults, found that a needle in the arm was 67 percent to 77 percent successful at preventing the flu, depending on the measurement method. The nasal spray was 30 percent to 57 percent effective.

Flu shots contain killed flu viruses. FluMist, approved in 2003, delivers weakened live viruses.

“This study suggests that maybe it doesn’t really offer any specific benefit beyond what you would get from just a regular flu shot, and under certain circumstances, it may not be quite as good,” said Dr. John Treanor, a vaccine expert at the University of Rochester Medical Center.

FluMist was designed with kids in mind, and an unpublished study sponsored by the company suggested it was more effective in youngsters than a shot in the arm, as measured by the children’s immune-system responses. But no one had conducted laboratory testing to compare the two methods head-to-head in adults.

In the study, volunteers were divided into four groups — those who got traditional flu shots made by Sanofi Pasteur, the vaccine business of France-based Sanofi-Aventis SA; those who got fake shots; those who received inhaled FluMist vaccines, made by MedImmune Inc. of Gaithersburg, Md.; and those who got fake nasal sprays.

The paper, by a team of University of Michigan researchers, was published in Thursday’s New England Journal of Medicine. The study was federally funded, but many of the researchers have consulted for vaccine makers.

Experts cautioned that the study, conducted in 2004-05, was done during a relatively mild flu season. Also, the vaccine that was formulated before the start of that season turned out to be poorly matched to the flu strains that dominated that winter.

Doctors had theorized that during poorly matched seasons, FluMist would be more effective. The theory is that because the inhalable vaccine uses a whole virus, it should trigger a more comprehensive immune system response than the dead virus components in the flu shot. Also, FluMist’s live virus engages the immune system in the nose's mucous membranes — where the flu virus hits — while the flu shot goes in the arm.

In the new study, both FluMist and flu shots offered protection, despite the mismatch between the vaccine and the dominant strains. The main difference was in how well the vaccines warded off B strains of flu. The two did about the same in warding off more serious A strains.

“We would not have predicted what we found,” said Dr. Arnold Monto, a study co-author.

As for why FluMist fell short of expectations, Monto said that because adults have had long exposure to flu viruses and flu vaccines, they probably do not have as dramatic an immune-system response to the live-virus vaccine as children do.

Some researchers downplayed the study's results, saying success against type B influenza is only a small victory.

“I don't put too much weight in that. Influenza B is not the major issue in influenza each year,” said Dr. William Schaffner, a preventive-medicine specialist at Vanderbilt University. He said he would not hesitate to recommend either vaccine to his patients.

FluMist is approved for healthy people ages 5 and 49. The flu shot is approved for people over 6 months of age.

In a separate study in the journal, University of Maryland researchers suggested that giving the company’s nasal spray vaccine to children might help control the spread of flu.

The study, funded by MedImmune, involved children from 24 public elementary schools in Maryland, Texas and Minnesota, and four private schools in Washington. People in the homes of vaccinated children reported fewer flu symptoms. However, hospitalizations and school absenteeism rates were about the same.

An accompanying editorial said the study was not conclusive, because parents knew whether their children had received vaccine; that can create bias in the way they report symptoms. Also, no lab tests were done to confirm that reported illnesses were actually the flu.

The flu leads to about 36,000 deaths and 200,000 hospitalizations each year, according to federal officials.

Copyright 2006 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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