Why do children 6 months through 9 years old require two doses of the H1N1 vaccine?
Young children are especially susceptible to disease because their immune systems have not built up the necessary defenses to fight infections. Vaccine effectiveness studies for seasonal flu have shown that 2 doses are needed to provide adequate protection during the first season that young children are vaccinated. The same study results can be applied to the H1N1 vaccine for children 9 years and younger.
