Resume : 2つの方法を利用した風疹のワクチン接種の優先的接種のモデル化 (第13回生物数学の理論とその応用 : 連続および離散モデルのモデリングと解析)

Resume:

2つの方法を利用した風疹のワクチン接種の優先的接種のモデル化

Hiroshi Nishiura

Department

of

_Hygiene

GraduateSchool of Medicmine

Hokkaido

_University

Resumeof

_forthcoming

article

Asan

original study

is

expected

tobe

_printed

_elsewhere,

herewithaResumeofthe

study

is

_provided

forthis

_proceedings.

Background

Rubella isa

contagious

viral

disease,

caused

by

rubella virus and

directly

transmitted from humantohuman. The infection is often mild and

_symptoms

laston

averagefor 1 to3

_days.

_However,

if

_pregnant

women areinfected

during

their

early

gestational

age

ofpregnancy,

the infectioncould also influence

fetus,

leading

toa cause of

_congenital

rubella

_syndrome

_(CRS).

OnceCRS occurs,itinducesserious incurable illness and about 20% of CRS is consideredtoresultin

_miscarriage.

For thisreason, adolescent femalehasbeena

_target

ofroutine immunizationas soonasthe vaccinewas

developed.

Later,

industrialized nationshave aimedtoelevate herd

_immunity

sothat the

epidemic

itselfcanbecontrolled.

Nevertheless,

an

epidemic

ofrubellawas seenfrom

2013‐15,

involving mostly

adults, especially

adult males.Itisa

tragedy

thatas_manyas 45 CRScaseshave been confirmed and notifiedtothe

_govemment.

The

_epidemic

wasconsideredtohave been caused

_by

a

policy

failure of

previous

vaccination program that has led the_present

day

30s‐50s male

_susceptible

torubella.Nowaneffective

supplementary

vaccination program hastobe

considered,

and such program hastobe

_{supported by objective}

scientific evidenceasassisted

by

mathematical models. When

considering

the

supplementary

vaccination and revaccination among

susceptible

pockets

in

_adults,

itis vitalto

_identify

themostcost‐effective

_strategy

ofvaccination. This is

_particularly

the casewhenan

epidemic

sporadically

_occurs,because the

_country

wouldnothave sufficient stock of vaccinestobe

_put

into

_place.

The purposes of the

present

study

weretwo‐fold. Onewasto

_identify

themost economical vaccination

_strategy,

_anticipating

similar future rubella

_epidemics.

The otherwastoestimate the

_required

minimum vaccination dosestoensurethatthe

major

epidemic

wouldnot

_happen.

数理解析研究所講究録

Method

Modeling

strategy

Usming

amathematical

model,

wereconstructthe transmission

dynamics

ofrubella in 2012‐13 anduseitfor

planning

futurecontrol. Thereweretwotasks.Onewasto

characterize the_ageand

_{gender specific}

transmission

_dynamics.

We

_employed

theso‐ called multivariate renewal process,

i.e.,

c_{aI} =s_{ai}(t)\displaystyle \sum_{j}2^{R_{abij}}\int_{0}^{t}c_{bj}(t-s)g(s)ds

todescribe the

_temporal

evolution ofrubella

_epidemic.

Theotherwasto

_implement

_multiple

scenarios

_varying

targethost of

supplementary

vaccination and revaccination. Model

_{parameterization}

Thewayto

_{identify susceptible}

individuals

_by

_ageand

_gender

has

_posed

a

problem

in

defining

the

_baseline,

because

_susceptibles

canbe

manually

identified intwodifferent ways.Oneisto trust

_{seroprevalence}

_data,

as

indicating

the fraction

protected.

Theother isto

_{explicitly quantify}

thenext

_generation

matrix usin_\mathrm{g}the_age and

_gender

stratified data.Forboth

_methods,

wehave used the age‐ and

gender‐specific

contactrates. Results/Discussion

Analyzing

bothcases,weshowed that

vaccinating

30\mathrm{s}male is

optimal.

Toachieve

optimal

vaccination,

the

_{supplementary}

vaccination and revaccination shouldnot involve female and shouldnotinvolve40\mathrm{s}male. Itwasalso shown that

securing

7.4 million vaccines would

_help

reduce the

_reproduction

numbertobe below1.0. Address for

_{correspondence:}

Department

of

_Hygiene

Graduate School of Medicin\mathrm{e} Hokkaido

_University

Sapporo

060‐8638 JAPAN

\mathrm{E}‐mail address:

_{nishiurah@med.hokudai.ac.jp}

北海道大学大学院医学研究科 西浦 博

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