Estimation of measles vaccine coverage needed to prevent transmission in schools.
BACKGROUND
The aim of the present study was to produce the first estimation in Japan of the basic reproduction number (R(0)) and the minimum level of vaccine coverage needed to prevent measles outbreaks (P(c)).


METHODS
A questionnaire survey was conducted during two measles outbreaks among 12-15-year-old middle school students in one prefecture in spring, from the end of February to the beginning of May 2002, and a stochastic mathematical model was constructed to calculate vaccine effectiveness (VE) and the basic reproduction number (R(0)). P(c) was calculated from R(0) and VE.


RESULTS
In outbreak 1 (school A), 62 (94%) of 66 patients responded to the questionnaire. Of a total of 601 students, 534 (88.9%) responded. Of these, 82.6% (441/534) had previously received measles vaccine. In outbreak 2 (school B), 20 (99%) of 21 patients responded. Of a total of 375 students, 373 (99.5%) responded. Of these, 317 (85.0%) received measles immunization. Mathematical analysis was as follows: in outbreak 1 R(0) was 7.40 (95% confidence interval [CI]: 7.36-7.44) and VE was 76.55% (95%CI: 53.24-87.54). In outbreak 2, R(0) was 18.89 (95%CI: 18.88-18.90) and VE was 98.54% (95%CI: 94.89-99.73). Consequently, P(c) was 112.97% (95%CI: 92.29-145.52) in outbreak 1 and 96.11% (95%CI: 93.81-98.53) in outbreak 2.


CONCLUSIONS
Because of the lower VE in outbreak 1, measles virus transmission could not have been stopped even if all students received a single dose of vaccine. In outbreak 2, with higher VE, the outbreak could have been prevented by increasing the proportion of students who had been vaccinated.
Mori
Nobuo
N
Field Epidemiology Training Program, Infectious Disease Surveillance Center, National Institute of Infectious Diseases, Tokyo, Japan. morin@takii.kmu.ac.jp
Ohkusa
Yasushi
Y
Ohyama
Takaaki
T
Tanaka-Taya
Keiko
K
Taniguchi
Kiyosu
K
Kobayashi
John M
JM
Doy
Mikio
M
Okabe
Nobuhiko
N
D000293:Adolescent; D002648:Child; D004196:Disease Outbreaks / Q000517:prevention & control; D006801:Humans; D008433:Mathematics; D008457:Measles / Q000517:prevention & control* / Q000635:transmission; D008458:Measles Vaccine / Q000276:immunology*; D008962:Models, Theoretical; D012572:School Health Services; D011795:Surveys and Questionnaires; D014611:Vaccination
D008458:Measles Vaccine