Effectiveness assessment of vaccination policy against measles
epidemic in Japan using an age–time two-dimensional
Yusuke Maitani•Hirofumi Ishikawa
Received: 14 February 2011/Accepted: 8 April 2011/Published online: 7 May 2011
? The Japanese Society for Hygiene 2011
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.
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 discrimi-
nated 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 vac-
cination policies on the prevention of a measles epidemic.
The results of this quantitative study indicated
that suppression of a measles outbreak requires the main-
tenance of high vaccine coverage and that a decline in
vaccine coverage may result in a measles epidemic.
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 vac-
cination as scheduled should be accompanied by endeavors
In 2007, measles prevailed among the youth
to maintain appropriate high vaccine coverage of the first
and second stages.
Routine immunization program ? Age–time model ?
Measles ? Vaccination coverage ?
In 2007, measles prevailed among the youth and young
adult (teenagers and those in their 20s) population of Japan,
creating serious social problems, such as closure of college/
university classes. The incidence of measles in Japan has
been reported to be 10,000–30,000 per year , but the
actual incidence is estimated to be about tenfold higher
than the number of reported cases . The aim of this study
was to analyze the effect of improvements to the standard
vaccination program for measles, with a special focus on
the coverage of measles vaccination. Vaccination against
measles was incorporated into the national immunization
program in Japan in 1978, but in 1994 some children had
an allergic reaction due to sensitization to the gelatin
contained in the measles–mumps–rubella vaccine (MMR).
As a consequence, the measles vaccination policy was
modified, i.e., from mass immunization in schools to
individual immunization, and from obligatory to voluntary
immunization. This policy change has led to the ongoing
low vaccination coverage against measles that was imme-
diately detectable . Because it is feared that an outbreak
of measles will occur under these circumstances, a second
stage of measles vaccination was introduced into the rou-
tine immunization program in 2006. In 2008, a third and
fourth stage of measles vaccination were later added to the
routine immunization program for a limited period of
Y. Maitani ? H. Ishikawa (&)
Department of Human Ecology,
Graduate School of Environmental Science,
Okayama University, Okayama 700-8530, Japan
Environ Health Prev Med (2012) 17:34–43
5 years (2008–2012). The first to fourth stages of vacci-
nation were targeted at infants (1 year old), children 1 year
prior to starting elementary school (5–6 years old), students
in the first grade of junior high school (12–13 years old),
and students in the third grade of high school (17–18 years
old), respectively . Those autonomous local and regional
authorities that achieved high vaccination coverage in the
second stage did so by encouraging individual vaccination,
establishing a strong partnership with institutions, distrib-
uting leaflets, mailing postcards, posting notifications of
vaccination on city bulletin boards and posters, and
developing a system to target non-vaccinated individuals,
among others (Niigata, Odawara, Takamatsu, and Kura-
shiki cities, and Fukui and Akita prefectures) [3–8]. Those
authorities that achieved high vaccination coverage in the
third and the fourth stages had a program that involved
notification of individuals for vaccination, cooperation with
schools, and mass immunization against measles, among
others (Johetsu, Tsukuba, Hakodate, and Hamamatsu cit-
The World Health Organization (WHO) assesses the
numbers of measles patients and deaths attributable to
measles to be more than 30,000,000 and 875,000 each year,
respectively . In most developed countries, including the
USA and Korea, the law obliges parents to present a cer-
tificate of measles vaccination when their child enters
elementary school , which has resulted in a high vac-
cination coverage. Consequently, any outbreaks of measles
in such countries mainly occur among immigrants from
regions where measles is epidemic.
In recent years, most individuals have acquired immu-
nity to measles by vaccination. Because the antibody titer
acquired by vaccination is low compared with that by nat-
ural infection, the possibility of re-infection with measles
emerges in teenagers and in young adults in their 20s .
There have been several studies on a mathematical
model for the transmission of measles [15–20]. In this
study, we 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. We
analyzed vaccination policy and the influence of vaccina-
tion coverage through model simulations. To make the
model more precise, we developed the model to be able to
distinguish maternal immunity derived from a mother who
acquired immunity by natural infection from that derived
from a mother who acquired immunity by vaccination
because most mothers have acquired the antibody against
measles by vaccination in recent years. We also used epi-
demiological classes comprising individuals with low
antibody titer so as to be able to estimate the change in the
number of individuals with low antibody titer because any
increase in the number of such individuals may cause an
outbreak of measles.
The results of simulation indicated that the suppression
of a measles outbreak requires the maintenance of high
vaccine coverage, that a decline in vaccine coverage may
cause a measles epidemic, and that the present routine
immunization program of measles will maintain a low risk
of an epidemic even after discontinuation of the third and
fourth stages as scheduled—as long as at least 90% vaccine
coverage of the first and second stages is maintained.
Materials and methods
Okayama city, the capital of Okayama prefecture (popu-
lation 674,746 in 2005 ), was almost equivalent in
terms of vaccine coverage against measles to Japanese
national average, and Kurashiki city in Okayama prefecture
(population 469,377 in 2005 ) achieved high vaccine
coverage in the second vaccination of measles [22, 23].
Okayama city and Kurashiki city were chosen as targeted
regions in this study. The levels of measles vaccine cover-
age in Okayama city, Kurashiki city, and the mean coverage
of the whole country in 2008 are shown in Table 1.
Progress in symptom of measles
The clinical symptoms of measles progress from catarrh
(2–4 days) to rash (3–4 days), and then to a convalescence
period (3–4 days) after a latent period of 8–12 days [24,
25]. Any severe complication, such as brain inflammation
or pneumonia, may cause patient mortality. In this study,
we adopted 5 days as the infection period and 10 days as
the latent period, while we adopted 10 days as the infection
period and 16 days as the latent period for modified mea-
sles patients [24, 25].
Maternal immunity declines approximately 6 months after
birth on average . A study on the antibody titer of
Table 1 Mean percentage of vaccination coverage (from April 2008
to March 2009)
LocationStage of routine immunization by measles
First (%) Second (%)Third (%)Fourth (%)
Okayama city 92.994.690.477.9
Kurashiki city 96.395.788.976.3
Derived from National Institute of Infectious Diseases, 2008 [22, 23]
Environ Health Prev Med (2012) 17:34–4335
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