Curiosities: How do public health officials determine which strain of influenza to create vaccines for each year?

This year’s influenza vaccine in the United States contains three strains of the influenza virus. Last March, experts at the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization chose those strains based on the varieties of flu virus that were present at the end of North America’s flu season.

The decision also took into account viruses found in Australia, South Africa and the tip of South America. “These countries were at the very beginning of the influenza season, when we wee at the tail end,” says Jonathan Temte, an associate professor of family medicine at UW–Madison.

Temte, who is a member of the CDC’s Advisory Committee on Immunization Practices, says jet planes are a virus’s best friend. A person, and any virus they carry, “can reach Wisconsin from anywhere in the world in less than one incubation period [one to three days].”

There is no guarantee that the vaccine will contain the exact strain of flu that is causing fevers, coughs, sore throats, aches and pains next winter, but an imperfect vaccine can still help, Temte says. “In general, if you were immunized with a mismatched vaccine, you would be still be less likely to contract the flu than if you were not immunized.”

Because the benefits of flu vaccine so greatly outweigh the minimal risks, experts say about 83 percent of the population, including virtually all people under age 18 or over age 50, should get vaccinated.

Now is the time to stand up and get your vaccine, Temte says.