Abstract
In 2018-2019, New York City experienced the largest measles outbreak in the United States in nearly three decades. To identify key contributing factors, we modeled the transmission dynamics of this outbreak. Results indicate that delayed vaccination of 1- to 4-year-olds enabled the initial spread and that increased infectious contact, likely via "measles parties," facilitated later transmission. We found that around half of infants were susceptible by age 1 and thus had many infections. Without the implemented vaccination campaigns, numbers of infections and hospitalizations could have been >10 times higher and would predominantly affect those under 4. These results suggest that a first vaccine dose before age 1 and the second dose before age 4 could allow parents to vaccinate and protect children more effectively should a high level of vaccine hesitancy persist. Enhanced public health education is needed to reduce activities that unnecessarily expose children to measles and other infections.