MARSHFIELD, Wis. – Influenza has hit the U.S. hard this winter, but early estimates show the vaccine significantly reduces the risk of getting the flu, according to a national report released today.
The vaccine, which protects against two influenza A and one influenza B virus strains, is 62 percent effective so far this season, according to a report from the U.S. Flu Vaccine Effectiveness Network, which includes the Marshfield Clinic Research Foundation in Marshfield, Wis. The Centers for Disease Control and Prevention (CDC) supports the network.
"The take home message is that the flu vaccine is moderately effective this year, and people who are vaccinated have about a 60 percent 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, an epidemiologist and a lead researcher on the report. He also serves as director of the Epidemiology Research Center at the Marshfield Clinic Research Foundation.
The effectiveness of the flu vaccine can vary from year to year due to changes in the flu viruses and vaccine components.
The estimated effectiveness against influenza A was 55 percent and against influenza B it was 70 percent effective, the report said. The final effectiveness estimates may vary from the early-season report. The early vaccine effectiveness in 2013 is 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 CDC. The predominant type of flu circulating in the U.S. is H3N2 influenza A virus, according to the report. 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 said. “The CDC recommends that anyone who has not already been vaccinated should get the vaccine.”
Although it takes about two weeks to be fully protected, the flu season began early and likely will continue for weeks. Getting vaccinated now can provide additional protection if the season continues through February and into March.
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 Dec. 3 and Jan. 2. In Marshfield, testing began in mid-December, and more than 500 patients have been enrolled. About 50 percent of those tested were positive for one of the flu viruses.
There have been multiple reports of flu cases 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.
The Marshfield Clinic Research Foundation was the first site to receive CDC funding to study influenza vaccine effectiveness, and was the sole provider of this information for four flu seasons beginning in 2004-2005.