The current influenza season, dominated by the A H3N2 virus, continues to be active, though it's on the downswing across the nation, says the Centers for Disease Control and Prevention (CDC). Data collected by the CDC show this season's influenza vaccine is 48 percent effective in preventing influenza. Dr. Pritish Tosh, an infectious diseases specialist at Mayo Clinic, says researchers use this information to determine the upcoming season's influenza vaccine. Dr. Tosh says, "The viral strains that are being predicted and recommended for the upcoming vaccines, which are similar to what we had the previous year, with exception of the H1N1 component of the vaccine, will use a slightly different viral strain."
Journalists: Sound bites with Dr. Tosh are in the downloads.
"The way that the strain is to be contained in the vaccine is determined through international surveillance for circulating influenza strains," says Dr. Tosh. "There are many places throughout the world that are collecting influenza strains and finding out what’s circulating in different areas. The World Health Organization and the CDC look at these trends, and what is being found in different areas, and try to predict the likely influenza strains that are going to come in the following season."
"It takes time to develop the vaccine — from the point you identify the strain to the point that you’re actually growing it in eggs in sufficient quantities, and then able to do your quality control," says Dr. Tosh. "Rather than identifying closer to the influenza season, because of the necessity of how the vaccine is made, that call has to be made months — up to six months — ahead of time to give the manufacturers plenty of lead time in order to make sufficient amounts of influenza vaccine to be ready for the population."