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

Tuesday, 26th of November 2013

[source]Environmental Health and Preventive Medicine[|source]

In recent years, most individuals have acquired immunity to measles by vaccination. Because the antibody titer acquired by vaccination is low compared with that by natural infection, the possibility of re-infection with measles emerges in teenagers and in young adults in their 20s. 

In this article, the authors developed an age–time two-dimensional model for the transmission of measles to reflect an age structure, thereby enabling the selection of contact rate by age. This model was able to distinguish maternal immunity derived from a mother who acquired immunity by natural infection from maternal immunity derived from vaccination. The report documents that a) the suppression of measles outbreaks requires the maintenance of high vaccine coverage, b) declines in vaccine coverage may cause a measles epidemic, and c) present routine immunization program of measles will maintain a low risk of an epidemic as long as at least 90% vaccine coverage of the first and second stages is maintained. More details are available at:  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3258320/

 

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 endeavours to maintain appropriate high vaccine coverage of the first and second stages.