Behind the Scenes of the Flu Vaccine
How flu vaccine is made each year -- and whether it will protect us this time.
Sept. 19, 2008— -- Each year, millions head to their doctors' offices for a shot to protect them from the strains of influenza that keep many in bed sick come the winter months.
Simply developing that vaccine is a complicated process, involving guesswork, observation and even a trip to the farm.
The process actually begins in February, as scientists from the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) select the strains of flu virus they expect to be most prevalent in the upcoming year.
Typically they are chosen based on the most prevalent strains in the southern hemisphere during their flu season in the months prior, according to CDC spokesperson Arleen Porcell.
But as past years have shown, selecting the right strains is not a perfect science.
"There's a certain amount of science and a certain amount of art to it," said Stephen Morse, an epidemiologist at the Mailman School of Public Health at Columbia University.
According to Dr. Andrew Pavia, chair of public health committee of the Infectious Diseases Society of America and a professor of professor of pediatrics at the University of Utah, the vaccine has been a good match 18 of the past 21 years.
"Some years the predictions are not perfect," he said.
Because of the WHO involvement in the annual meeting, vaccinations are relatively standard everywhere during our flu season.
"Wherever you get it in the Northern Hemisphere, if it's been made properly, it will be identical," he said.
Ultimately, three strains of influenza virus are chosen for the vaccine: a variant of H1N1, a variant of H3N2 (both influenza A viruses) and a strain of the influenza B virus. Influenza A viruses are the strongest, and vary the most from year to year, while B viruses rarely make anyone but the most vulnerable people sick.
Influenza C viruses are not part of the vaccine, largely because they rarely vary and typically physicians think it would be better to just develop immunity from catching it, said Morse.
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