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Current Flu Vaccine About 60% Effective

H3N2 influenza A is predominant circulating strain (Jan. 11)

The current flu vaccine — which protects against two influenza A and one influenza B virus strains — is 62% effective so far this season, according to a report from the U.S. Flu Vaccine Effectiveness Network.

“The take-home message is that the flu vaccine is moderately effective this year, and people who are vaccinated have about a 60% lower risk of getting the flu compared to someone who is not vaccinated. It’s a safe vaccine that can help prevent the flu and its complications in both children and adults,” said Dr. Edward Belongia, lead researcher on the report. He also serves as director of the Epidemiology Research Center at the Marshfield Clinic Research Foundation in Marshfield, Wisconsin.

The current vaccine was estimated to be 55% effective against influenza A and 70% effective against influenza B. These early findings are similar to the level of effectiveness reported in other recent flu seasons and in clinical trials of flu vaccines.

The rate of influenza cases began to increase rapidly in December, marking the flu season’s earliest start in a decade, according to the Centers for Disease Control and Prevention (CDC). The predominant type of flu virus currently circulating in the U.S. is H3N2 influenza A. Seasons dominated by the H3N2 strain tend to be more severe, with a greater number of hospitalizations and deaths, Belongia said.

“This is the most severe flu season we’ve seen in Wisconsin since 2008, when the H3N2 strain was also common,” Belongia remarked. “The CDC recommends that anyone who has not already been vaccinated should get the vaccine.”

Although it takes about 2 weeks to be fully protected after vaccination, the flu season began early this season and likely will continue for weeks. Getting vaccinated now can provide additional protection if the season continues through February and into March, the report says.

It’s particularly important for young children, pregnant women, the elderly, and people with chronic health conditions to get vaccinated, because they have the highest risk of serious illness, hospitalization, or death from the flu.

For the report, researchers looked at data from 1,155 children and adults who had acute respiratory infections between December 3 and January 2. In Marshfield, testing began in mid-December, and more than 500 patients were enrolled. About 50% of those tested were positive for one of the flu viruses.

Numerous cases of flu have been reported in people who were vaccinated this year. According to Belongia, it’s not uncommon to see flu cases in vaccinated people, and physicians should not base their treatment decisions on whether a person has been vaccinated. The CDC recommends initiating antiviral treatment as soon as possible for people who are seriously ill with influenza or at high risk for complications.

“While the flu vaccine is the best intervention we have at this time, there is a need for more research to develop a new generation of influenza vaccines with even higher and longer-lasting protection,” Belongia said.

Source: Marshfield Clinic Research Foundation; January 11, 2013.

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