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Flu Vaccines Compared

Dec. 13, 2006 -- Wondering how flu vaccines compare at flu prevention?

A new study of healthy adults shows that the flu shot worked better than the nasal-spray flu vaccine during the 2004-2005 flu season.

But don't jump to conclusions about which type of flu vaccine is better.

"In other years the results may be different," says Arnold Monto, MD, in a University of Michigan news release.

Monto is a University of Michigan epidemiology professor.

The study by Monto and colleagues appears in The New England Journal of Medicine.

About Flu Vaccines

The single best way to protect against the flu is to get vaccinated each year, states the CDC's web site.

There are two types of flu vaccines: the flu shot and the nasal-spray flu vaccine.

The flu shot contains killed flu viruses. It's approved for people older than 6 months, including healthy people and people with chronic medical conditions.

The nasal-spray flu vaccine is made with live, weakened flu viruses that don't cause the flu. The nasal-spray flu vaccine is approved for use in healthy people aged 5-49 who aren't pregnant.

The CDC doesn't recommend one type of flu vaccine over the other for people who are eligible for either type of vaccine.

Flu Viruses, Flu Vaccines

Flu viruses change all the time. Every year, scientists tailor flu vaccines to target flu viruses that are predicted for the upcoming flu season.

But those predictions aren't always perfect. And that's what happened during the flu vaccine study.

During the 2004-2005 flu season, when the flu vaccine study was under way, most flu viruses didn't exactly match either type of flu vaccine.

That mismatch may have affected the vaccines' effectiveness, the researchers note.

Flu Vaccine Study

Monto's team studied 1,247 healthy adults aged 18-46 (average age: 27) during the 2004-2005 flu season.

Participants either got the flu shot, the FluMist nasal-spray flu vaccine, or an empty vaccine (placebo).

Very few people -- 32 participants -- came down with confirmed flu during the 2004-2005 flu season.

Lab tests showed that the flu shots were 77% effective against the flu, compared with 57% effectiveness for the nasal-spray flu vaccine.

The spray may have been particularly ineffective against unexpected type B flu viruses during that flu season, but that's not certain, the researchers note.

They add that other studies have shown the nasal-spray flu vaccine's effectiveness in children.

Flu Vaccine Knowledge Lacking

"We need a more specific understanding of which viral changes matter and which don't," Monto says.

"There are many things about vaccine protectiveness that we still don't completely understand," he says.

It's not clear if the study's findings apply to other groups of people, so further studies are needed, notes a journal editorial.

The editorialists are Keiji Fukuda, MD, MPH, and Marie Paule Kieny, PhD, of the World Health Organization.

FluMist was developed at the University of Michigan and is produced by MedImmune under a license with the university, according to a University of Michigan news release.

In the journal, Monto notes having received consulting fees from drug companies including MedImmune. MedImmune is a WebMD sponsor.