Data from a randomized, controlled trial demonstrated that children 6 months to less than 3 years of age had diminished hemagglutinin inhibition (HAI) responses to Flublok as compared to a U.S.-licensed influenza vaccine approved for use in this population, strongly suggesting that Flublok would not be effective in children younger than 3 years of age. Safety and effectiveness of Flublok in children 3 years to less than 18 years of age have not been established.