Effectiveness assessment of vaccination policy against measles epidemic in Japan using an age–time two-dimensional mathematical model

Abstract

Objectives In 2007, measles prevailed among the youth and young adult population in Japan, creating in a serious social problem. Among the developed countries, Japan has a relatively high incidence of measles. The objective of this study was to assess the effect of improvements in the vaccination policy against measles through simulations. Methods We developed an age-time two-dimensional model for the transmission of measles to reflect an age structure, enabling contact rate to be selected by age. Introduction of the maternal immunity class into the model allowed natural infection and vaccination to be discriminated along the course of an infant's mother acquiring the immunity, thereby resulting in an improved accuracy of the simulations in infants. Several vaccination scenarios were attempted in order to assess the influence of various vaccination policies on the prevention of a measles epidemic. Results The results of this quantitative study indicated that suppression of a measles outbreak requires the maintenance of high vaccine coverage and that a decline in vaccine coverage may result in a measles epidemic. Conclusions The present standard immunization program for measles will maintain an acceptable level of immunity and is therefore associated with a low risk of an epidemic after discontinuation of the third and fourth stages as scheduled-as long as at least 90% vaccine coverage of the first and second is maintained. The simulation results show that discontinuation of the third and fourth stages of vaccination as scheduled should be accompanied by endeavors to maintain appropriate high vaccine coverage of the first and second stages.

Evolution and Use of Dynamic Transmission Models for Measles and Rubella Risk and Policy Analysis

“…Overall, 16 models (12%) considered waning immunity and reinfection for measles, rubella, or measles and rubella . The first studies that considered waning immunity explored the concept in the context of sensitivity analyses (i.e., not part of the primary analysis) assuming some individuals wane to become fully susceptible .…”

“…Subsequent studies assumed individuals with waned vaccine‐induced immunity became fully susceptible (i.e., same infectiousness and duration of infection as fully susceptible individuals) or partially infectible (i.e., less severe infection and shorter duration of infectiousness) . Two studies modeled immunity as a function of antibody concentrations and independent of the nature of immunity (i.e., infection induced or vaccine induced) . Finally, based on observed loss of measles immunity of vaccinated children with HIV, one study used inputs from several African countries to suggest that HIV did not change transmission dynamics in the absence of antiretroviral therapy (ART), but the introduction of ART led to increased survival and increased expected measles cases .…”

Low titers of measles antibodies in Japanese pregnant women: A single‐center study

“…16 The second reason is that the antibody titers in response to measles vaccination have been reported to be lower than those in response to natural infection with the measles virus. 7,17 In Japan, measles is not a common disease, and in the majority of the population, measles immunity has been acquired as a result of measles vaccination rather than as a result of natural infection. It is speculated that low antibody titers acquired through vaccination may have been responsible for the significant population with low-positive titers in our study.…”

“…The prevalence of measles infection has decreased dramatically on a worldwide scale after the launch of the measles vaccination program. However, in Japan, local epidemics of measles and cases of measles during pregnancy continue to be reported, and the seroprevalence of antibodies to measles virus in Japanese pregnant women, which has not been reported, is suspected to be unsatisfactory 1,6–8 …”

“…However, in Japan, local epidemics of measles and cases of measles during pregnancy continue to be reported, and the seropreva-lence of antibodies to measles virus in Japanese pregnant women, which has not been reported, is suspected to be unsatisfactory. 1,[6][7][8] Several methods have been reported for the detection of measles-specific immunoglobulin G antibody. The neutralization test (NT) is one of the most reliable methods to determine the degree of immunity against measles 9,10 and has been used to evaluate the accuracy of several other methods, including the enzyme-linked immunosorbent assay (ELISA), hemagglutination inhibition test (HI), and the particle agglutination test (PA).…”