TRANSMISSION DYNAMICS OF AND INSIGHTS FROM THE 2018-2019 MEASLES OUTBREAK IN NEW YORK CITY: A MODELING STUDY
In 2018-2019, New York City experienced the largest measles outbreak in the US in nearly three decades. To identify key factors contributing to this outbreak to aidfuture public health interventions, here we developed a model-inference system to infer the transmission dynamics of measles in the affected community, based on incidence data. Our results indicate that delayed vaccination of young children aged 1-4 years enabled the initial spread of measles and that increased infectious contact among this age group, likely via gatherings intended to expose unvaccinated children (i.e. “measles parties”), further aggravated the outbreak and led to widespread of measles beyond this age group. We found that around half of infants were susceptible to measles by age 1 (the age-limit to receive the first vaccine dose in the US); as such, infants experienced a large number of infections during the outbreak. We showed that without the implemented vaccination campaigns, the outbreak severity including numbers of infections and hospitalizations would be 10 times higher and predominantly affect infants and children under 4. These results suggest that recommending the first vaccine dose before age 1 and the second dose before age 4 could allow pro-vaccine parents to vaccinate and protect infants and young children more effectively, should high level of vaccine hesitancy persist. In addition, enhanced public health education is needed to reduce activities that unnecessarily expose children to measles and other infections.
MEASLES SPATIAL SPREAD ACROSS CHINA DURING 2005−2014
Measles is a highly infectious and severe disease – it is a leading cause of death in children in developing regions, killing 114,900 globally in 2014. Elimination of the disease can nevertheless be achieved with vaccination of 90-95% of a population, as shown in theory and practice. In China, however, measles continues to infect thousands of people each year despite vaccination coverage above 95%. This conundrum challenges measles elimination in China and worldwide. In this study, we characterize the geospatial distribution of measles and epidemic connections among cities across China. Using incidence data reported during 2005-2014 for all 344 cities, we show that the municipal burden of measles differed substantially and some cities were highly connected and experienced synchronous outbreaks. We identify 14 cities that experienced endemic transmission during 2005−2010, and 21 transmission clusters, including 6 cross-regional clusters that link the less developed inland regions and the industrial east. We find that three transmission foci coexist in China—cities with large minority populations, inland cities with more emigrants, and mega industrial cities hosting more immigrants—and that migrant workers, connecting the latter two foci, likely facilitate measles transmission across regions. This complex connection, along with the differing disease burden among cities, renders measles elimination challenging in China despite the high overall vaccination rate. Future immunization programs should therefore target these three foci.
LONG-TERM MEASLES EPIDEMIC DYNAMICS IN CHINA AND IMPLICATIONS FOR ELIMINATION
Despite high vaccine coverage, measles continues to cause large epidemics in China, a country currently supporting 18% of the world’s population. To improve understanding of this phenomenon, in this study, we develop a comprehensive model-inference system; using this system, we are able to simulate measles epidemic dynamics and estimate key epidemiological characteristics in three key locations in China during 1951-2004, a period that spans the pre-vaccine and modern mass-vaccination eras. These estimates include spatiotemporal variations in population susceptibility and the basic reproductive number (R0), an epidemiological parameter commonly used to inform target vaccination levels for measles elimination. Our findings reveal population and epidemiological characteristics crucial for understanding the current persistence of measles epidemics in China and for devising future elimination strategies.