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Flu Shot Beats Flu Spray for Young Adults

Study: Adults 18-49 Who Got the Shot Half as Likely to Get Flu
WebMD Health News
Reviewed by Louise Chang, MD

Sept. 23, 2009 -- The traditional flu shot beats out the newer flu nasal spray in young adults aged 18 to 49, according to a new study.

''Those who got the inactivated vaccine [the traditional flu shot] were half as likely to get the flu as those who got the live attenuated vaccine [the flu nasal spray]," says the study's lead author Arnold Monto, MD, a professor of epidemiology at the University of Michigan School of Public Health in Ann Arbor. The study is published in the New EnglandJournal of Medicine.

Despite those results, Monto and other experts say that getting vaccinated against seasonal flu -- whether by the traditional injection or the newer nasal spray -- is better than getting no vaccine at all.

Flu Shot Beats Flu Spray: Study Details

For the study, Monto and his colleagues enrolled 1,952 healthy men and women, all aged 18 to 49, in the fall of 2007. They randomly assigned the participants to receive either the traditional vaccine, the nasal spray, or placebo, without the participants knowing if they were getting placebo or the actual vaccine.

They tracked the participants throughout the 2007-2008 flu season, and suspected cases of influenza -- marked by muscle aches, headache, nasal congestion, nausea, and vomiting -- were confirmed either by cell culture of the virus or by a highly sensitive test known as a PCR assay, or both.

Flu Shot Beats Flu Spray: Study Results

At the end of the study, 119 people had confirmed influenza. Those who got the injection had a 50% reduced chance of getting influenza compared to the group that got the nasal spray.

When the researchers looked only at the vaccines' effectiveness in preventing influenza A, the more common flu to infect the participants, the injection was 72% effective but the nasal spray just 29%.

Too few cases of influenza B were found to compare the vaccines, according to Monto. Funding for the study was provided by the National Institute of Allergy and Infectious Diseases and an unrestricted grant from Sanofi Pasteur, which makes the flu shot vaccine. MedImmune provided the nasal spray vaccine. Monto has received lecture fees from Sanofi Pasteur.

Flu Shot Beats Flu Spray: Study Implications

In recent years, studies comparing the two types of vaccines have produced mixed results, Monto says. ''Definitive studies have been done in children looking at the same comparison and they have found the live attenuated [nasal flu spray] outperforms the inactivated, and that's for children under age 6."

Why is that? ''The nasal spray vaccine works best in bodies which have produced fewer antibodies," Monto speculates. The virus in the nasal spray is attenuated, or weakened, and it must infect the nasal passages to trigger an immune response, the production of antibodies, which protects against infection by the virus.

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