Think globally, act locally: the role of local demographics and vaccination coverage in the dynamic response of measles infection to control

Abstract

The global reduction of the burden of morbidity and mortality owing to measles has been a major triumph of public health. However, the continued persistence of measles infection probably not only reflects local variation in progress towards vaccination target goals, but may also reflect local variation in dynamic processes of transmission, susceptible replenishment through births and stochastic local extinction. Dynamic models predict that vaccination should increase the mean age of infection and increase inter-annual variability in incidence. Through a comparative approach, we assess national-level patterns in the mean age of infection and measles persistence. We find that while the classic predictions do hold in general, the impact of vaccination on the age distribution of cases and stochastic fadeout are mediated by local birth rate. Thus, broad-scale vaccine coverage goals are unlikely to have the same impact on the interruption of measles transmission in all demographic settings. Indeed, these results suggest that the achievement of further measles reduction or elimination goals is likely to require programmatic and vaccine coverage goals that are tailored to local demographic conditions.

Post-Ebola Measles Outbreak in Lola, Guinea, January–June 20151

“…Although the case data are not exhaustive (n = 284), the database can be used to analyze transmission dynamics. The average and median age of case-patients was 2.8 years and 2.0 years, respectively, substantially lower than the mean age of infection of 5.6 years in Africa ( 10 ). Of 284 case-patients, 263 (92.6%) were 0–5 years of age, 17 (6.0%) were 6–15 years of age, and 4 (1.4%) were >15 years of age.…”

Age patterns and transmission characteristics of hand, foot and mouth disease in China

“…HFMD is not in this kind of situation. Estimates of transmission characteristics from standard approach have important applications: the age-specific force of infection can be used to identify age groups that have higher infection rates [19, 33] and can be applied as initial parameter values to dynamic models [21]; the average age at infection can be analyzed for impact factors of disease transmissions [40]. …”

Demographic transition and the dynamics of measles in six provinces in China: A modeling study

“…Increased vaccination coverage reduces the rate at which new susceptible individuals are added to the population; this has been described as a reduction in the “effective birth rate” as it has been shown to have equivalent consequences to a reduction in the absolute birth rate [12], which may increase the rate of local stochastic fadeout [14] or shift the dynamics from regular multi-annual cycles to episodic outbreaks [12,13]. Declining prevalence, due to vaccination [14,15] or reduced birth rate [16], decreases the per capita infection rate and raises the mean age of infection. The resulting increase in the mean age of the susceptible population may lead to a buildup of susceptible adults that can affect the dynamics of measles outbreaks [17,18].…”