A “flu shot” is different than other vaccines because the influenza virus is different. Vaccines against other viruses like measles, mumps, and chicken pox have stayed pretty much the same over the decades they have been in use. Influenza is different because it changes its shape almost continuously, and when it does, the vaccine against it loses its effectiveness. The biggest public health challenge of influenza is keeping up with the changes in the virus so that the vaccine that protects us against it can be updated to match.
There are 3 main types of influenza virus, also caused strains: Influenza A, Influenza B, and Influenza C. Influenza A causes most cases of influenza in humans, as well as the most severe. Most widespread epidemics, called pandemics have been caused by Influenza A. The most recent formulations of influenza vaccine contain 3 different strains of influenza: 2 strains of A and one strain of B. This will probably change next year because the FDA has just approved a new formulation that will allow a total of 4 strains in the vaccine.
How likely we are to become ill with influenza depends on whether we have been exposed to it before, and how effectively our immune system can respond to it.
When we come in contact with someone sick with influenza virus, we’ll be able to fight it off more effectively if we’ve encountered that particular strain before. This is because we have antibodies left over from our previous encounter with it. If we are exposed to a strain of influenza that is new to us, we’re more likely to become sick from it because we don’t have any antibodies left over to help us fight it, and have to start making them before we can fight back.
The flu vaccine will only protect us against the 3 specific strains of influenza that it contains. Once the virus changes, the vaccine doesn’t protect against the new strain as well. In order for the flu vaccine to continue to protect us, it has to be changed to match. To do this, we need to keep track of the influenza virus so that that we’ll know when it’s made another change. Since most new strains of influenza start in China, a nationwide network of surveillance is not enough. To keep up with influenza, you need a global network, like the one used by the World Health Organization, or WHO.
The WHO tracks currently circulating strains of influenza with over 100 influenza centers in more than 100 countries. These centers funnel information into five Centers for Reference and Research on Influenza, based in London, Melbourne, Tokyo, Beijing and Atlanta. These centers report on which flu viruses are currently circulating, identify newly emerging virus strains, and assess how these match up with current influenza vaccine components.
Which strains of influenza get included in our flu vaccine? The two main criteria used to decide which of the many strains of influenza circulating around the globe are included in the upcoming vaccine are the likelihood of a particular strain to cause significant illness in the United States, and the severity of the symptoms it causes.
Each February, the WHO meets to summarize the results of their ongoing global monitoring of influenza and to make recommendations of specific strains to include in flu vaccine formulas used in the Northern Hemisphere. They meet later in the year to select strains recommended for the Southern Hemisphere.
The WHO met in Geneva on February 23, 2012 to report on global influenza patterns and make recommendations for the Northern Hemisphere vaccine. Attending that meeting was a representative from the Center for Disease Control and Prevention (CDC), based in Atlanta. On February 28th, the CDC and the Food and Drug Association’s (FDA) Vaccines and Related Biological Products Advisory Committee voted on the exact formulation of our influenza vaccine.
The decision needs to be made as soon as reasonably possible, to allow time for vaccine makers to create the nearly 200 million doses that will be needed for the US population.
National Influenza Vaccination Week is December 2-8, 2012. Have you and your loved ones had their flu shot for this year? It’s not too late. Pharmacies and medical clinics have plenty of vaccine. Please contact them today to get your flu shot.
