As the flu season of 2012-2013 begins to wrap up, researchers are starting to analyze data to determine the effectiveness of vaccination against influenza. Remember, the flu vaccine is made months in advance, which means that experts from around the world study previous flu patterns and then decide which strains will likely be the most abundant the following flu season. Those strains are included in the vaccine, and it’s an educated guess at best.
The 2012-2013 influenza vaccine contained two A strains, H1N1 and H3N2, as well as a 2010 B strain. So how effective was this year’s vaccine?
Flu Season: Determining Vaccine Effectiveness
According to the Centers for Disease Control and Prevention (CDC) website, “vaccine effectiveness is a measure of how well the influenza vaccines work to protect against influenza infection and illness when they are used in routine circumstances in the community, and not specifically in a RCT [randomized control trial].” The CDC is basing vaccine effectiveness for this season on 2,697 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness Network from December 3, 2012 to January 19, 2013. During this time, the effectiveness of the influenza vaccine was 56 percent. This was a decrease from the first assessment, which found a vaccine effectiveness of 62 percent from December 3, 2012 to January 2, 2013.
2012-2013 Flu Vaccine Effectiveness: The Good News
The good news is that the 2012-2013 vaccine provided 58 percent protection from the most common and most serious H3N2 strain for children 6 months to 17 years of age. This season’s vaccine also provided 46 percent protection for those aged 18 to 49, and 50 percent protection for those aged 60 to 64. This means that the influenza vaccine kept a little over half of the people who were vaccinated from needing medical attention due to the flu. The flu vaccine generally protects between 50 and 60 percent of the people who are vaccinated.
Receiving the vaccine does not necessarily mean that you won’t get the flu, but if you do catch the flu, then the vaccine reduces your chances of having a severe case.
Vaccinating the Elderly: The Bad News
The bad news is that the influenza vaccine didn’t protect those over the age of 65 very well. According to the CDC, the vaccine effectiveness for those over the age of 65 was only 9 percent. So what happened? Reuters suggested that one reason for the low effectiveness could be due to the immune system in elderly people not reacting as strongly to the vaccine as a younger person’s immune system, but there is no definite research to show why the vaccine didn’t work as well in the elderly.
In the only large, randomized, controlled trial of influenza vaccination conducted in the elderly population (who were not in long-term care facilities), which was conducted during the 1991 – 1992 flu season, the vaccine effectiveness was 58 percent for people over the age of 65. So, clearly, something did not work with the 2012-2013 flu vaccine.
Even with different strains of the influenza virus circulating, the VE number should still be higher than nine percent; this reduced effectiveness has experts confused as well.
Flu Vaccine: Incomplete Data
The vaccine effectiveness numbers can change after the influenza season wraps up and more people are sampled. However, the numbers don’t look promising for those older than 65. There are still no answers as to why the vaccine was not effective for the elderly, but hopefully, once the season is over, the remaining questions will be answered.
Centers for Disease Control and Prevention. Interim Adjusted Estimates of Seasonal Influenza Vaccine Effectiveness – United States, February 2013. (2013). Morbidity and Mortality Weekly Report. Accessed February 23, 2013.
Centers for Disease Control and Prevention. Flu Vaccine Effectiveness. (2011). Accessed February 23, 2013.
Steenhuysen, J. In the U.S., flu vaccine worked in just over half of those who got it. (2013). Reuters. Accessed February 23, 2013.© Copyright 2013 Janelle Vaesa, MPH, All rights Reserved. Written For: Decoded Science