Measles outbreak in western Sydney. Vaccine failure or failure to vaccinate?
OBJECTIVE
To determine the effectiveness of measles vaccine during a measles outbreak, and to assess whether age at vaccination was a risk factor for measles vaccine failure.


METHODS
A matched case-control study.


METHODS
The five primary schools in western Sydney with the largest number of measles cases during the June to December 1993 outbreak.


METHODS
Seventy-nine children aged 5-9 years with an illness consistent with a clinical definition for measles. Two controls per case were selected from children in the same classroom.


METHODS
Estimated measles vaccine effectiveness by age of the child at vaccination and vaccination status: "unvaccinated"; "parental recall" (parents stated the child was vaccinated but no record could be found); and "record" (record including date of vaccination available).


RESULTS
The estimated vaccine effectiveness was 94% (95% confidence interval [CI], 83%-98%) in the "record" group, and 81% (95% CI, 46%-93%) in the "parental recall" group. Vaccine effectiveness did not differ significantly with age at vaccination (under 12 months of age 96% [64%-99%]; 12-14 months 95% [81%-99%]; and 15 months and over 93% [80%-98%]).


CONCLUSIONS
Vaccination records should be used to calculate a vaccine's effectiveness as parental recall may not be sufficiently accurate. The high vaccine effectiveness in the "record" group (94%) makes it unlikely that low vaccine effectiveness was the cause of the outbreak. More effort is needed to increase vaccine coverage to at least 95% in all population subgroups.
McDonnell
L F
LF
National Centre for Epidemiology and Population Health, Australian National University, Canberra.
Jorm
L R
LR
Patel
M S
MS
D000367:Age Factors; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D008297:Male; D008457:Measles / Q000453:epidemiology* / Q000276:immunology / Q000517:prevention & control; D008458:Measles Vaccine / Q000276:immunology*; D009517:New South Wales / Q000453:epidemiology; D012307:Risk Factors; D014611:Vaccination
D008458:Measles Vaccine