Dr. Sheng Li professor at the CUNY Graduate School of Public Health and Health Policy and colleagues, investigated the demographic transition and the dynamics of measles in six provinces in China.The work was published in the journal PLoS Medicine.
[Photo: Dr. Sheng Li]
Measles is a highly contagious childhood viral disease. Decades of increasing vaccination and development have led to dramatic declines in the global burden of measles, but the virus remains persistent in much of the world and is still an important cause of death among young children in developing countries. There has been a significant measles resurgence in past few years in Europe and North America, with New York City as disease hotspot. WHO’s Global Vaccine Action Plan has measles elimination by 2020 as a target, but achieving global elimination remains a significant public health challenge.
Using a novel time-varying catalytic model the research team fit three decades of age-specific measles case reporting in six provinces in China to quantify the change in the age-specific force of infection for measles virus over time. They further quantified the impact of supplemental vaccination campaigns on the reduction of susceptible individuals.
The force of infection of measles has declined dramatically (90-97 percent reduction in transmission rate) in three industrialized eastern provinces during the last decade, driving a concomitant increase in both the relative proportion and absolute number of adult cases, while three central and western provinces exhibited dynamics consistent with endemic persistence (24-73 percent reduction in transmission rate). The reduction in susceptible individuals due to supplemental vaccination campaigns is frequently below the nominal campaign coverage, likely because campaigns necessarily vaccinate those who may already be immune. The impact of these campaigns has significantly improved over time: campaigns before 2005 were estimated to have achieved less than 50 percent reductions in the proportion susceptible in the target age classes, but campaigns from 2005 onwards reduced the susceptible proportion by 32-87 percent.
The age distribution of measles cases changed in response to both demographic and vaccination processes. The research team combined both processes in a novel catalytic model, illustrating that age-specific incidence patterns reveal regional differences in the progress to measles elimination and the impact of vaccination controls in China. The research team concluded that the shift in the age distribution of measles susceptibility in response to demographic and vaccination processes emphasizes the importance of progressive control strategies and measures to evaluate program success that anticipates and react to this transition in observed incidence.