Estimating the Number of Measles-Susceptible Children and Adolescents in the United States Using Data From the National Immunization Survey-Teen (NIS-Teen).

Despite high measles vaccination rates in the United States, imported measles cases have led to outbreaks in the United States. These outbreaks have not led to sustained measles transmission; however, with each birth cohort of children not fully vaccinated against measles, measles-susceptible individuals accumulate in the population. The total number of measles-susceptible children and adolescents in the United States is unknown. We used age-specific measles vaccination data from the National Immunization Survey-Teen (2008-2013) to estimate the number of measles-susceptible children aged 17 years or younger, accounting for vaccine effectiveness, infant protection from maternal antibodies, and loss of immunity following childhood cancer treatment. Approximately 12.5% of US children and adolescents are susceptible to measles, with the highest levels of susceptibility being observed in children aged 3 years or younger (24.7% are susceptible to measles). In sensitivity analyses, we found that a sustained decrease in measles vaccination coverage from 91.9% (2013 level) to 90.0% (2009 level) would add nearly 1.2 million susceptible children and adolescents (thus making 14.2% of those aged 17 years or younger susceptible to measles). This reemphasizes the need for high measles vaccination coverage to support population-level immunity and prevent reestablishment of indigenous measles transmission in the United States.