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Flu Shot Beats Nasal Spray Flu Vaccine?

Military Recruits Who Got Flu Shot Had Fewer Doctor’s Visits for Influenza, Study Finds
By
WebMD Health News
Reviewed by Louise Chang, MD

March 2, 2009 -- The traditional flu shot, given as an injection in the arm, performs better than the newer nasal spray flu vaccine, shows a new study that compared the two vaccines in military personnel.

"We did find both vaccines effective," says study researcher Angelia Eick, PhD, a researcher at the Armed Forces Health Surveillance Center in Silver Spring, Md. The study is published in the early online edition of The Journal of the American Medical Association.

Because the study comparing the two vaccines was conducted among U.S. military personnel, it's not possible to make recommendations to the general population, Eick and co-researchers said at a telephone conference for reporters. But the results may help experts one day recommend one form of the flu vaccine over another.

Flu Vaccine Study: Details

Researchers compared the traditional influenza vaccine, first developed in the 1940s, to the intranasal spray vaccine, available since 2003, to no immunization at all.

The nasal spray flu vaccine contains live but weakened flu virus and is sprayed into the nostrils. It's approved for people aged 2 through 49 years. The flu shot is an inactivated or killed virus vaccine.

The researchers looked at three flu seasons -- 2004 to 2005, 2005 to 2006, and 2006 to 2007 -- and evaluated more than 3 million active-duty service members stationed in the U.S.

"They were all less than 50 years old, with no contraindications to vaccinate," says Zhong Wang, PhD, MPH, another study researcher and also a researcher at the Armed Forces Health Surveillance Center.

"We looked for the first health care encounter following the vaccination with a primary diagnosis code consistent with influenza or pneumonia," Wang says. That was the measure of vaccine effectiveness.

Flu Vaccine Study: Results

Those who got the shot in the arm were less likely to visit the health care system for influenza or pneumonia complaints, the researchers found.

Those who got the flu shot were 28% to 54% less likely to have a health care encounter than the unimmunized group, Wang says, and those who got the nasal spray flu vaccine were 10% to 21% less likely than the unimmunized group to have a health care visit for flu or pneumonia. Those results cover all three years, explaining the wide range, he says.

When they looked at vaccination history, the researchers found that the nasal spray vaccine had an effect similar to the flu shot in those who had not been vaccinated. That corresponds to some other study findings, the researchers note, that in healthy adults who are regularly immunized, the shot works better than the spray.

Flu Vaccine Study: Interpretations

"We need to keep in mind that this is one study," says Steven Tobler, MD, MPH, another study researcher and also a researcher at the Armed Forces Health Surveillance Center. "It certainly suggests that the trivalent inactivated vaccine [the flu shot] in a young healthy population might be more effective."

The study has limitations, Tobler says. For instance, the influenza cases were estimated by the visits in which the doctor's diagnosis was influenza or pneumonia, says Tobler, and the influenza cases were not confirmed in the laboratory.

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