This was a phase 4, randomized, double-blind, placebo-controlled study to evaluate the safety of 2 new 6:2 influenza virus reassortants in adults ages 18-49. There were 300 subjects enrolled at 2 sites in the US, 150 subjects at each site.
The FluMist Quadrivalent nasal spray vaccine, currently FDA approved, contains four different weakened flu virus strains. These viruses have been weakened so that they grow just enough to stimulate the immune system against flu but not enough to cause illness. This is similar to other vaccines you may have received as a baby. In the U.S., new wild-type flu strains that are to be used to produce the vaccine for the upcoming flu season are recommended annually to the FDA by an advisory board. For this year’s FluMist Quadrivalent, two new flu virus strains have been selected.