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Volume 6, Number 4—August 2000

Research

Reemergence of Pertussis in the Highly Vaccinated Population of The Netherlands: Observations on Surveillance Data

Hester E. de MelkerComments to Author , J.F.P. Schellekens, S.E. Neppelenbroek, F.R. Mooi, H.C. Rümke, and M.A.E. Conyn-van Spaendonck
Author affiliations: National Institute of Public Health and the Environment, Bilthoven, the Netherlands

Main Article

Table 2

Reported cases according to vaccination status and estimate of vaccine-effectiveness according to method of diagnosis

1- to 4- yr-olds Vaccine efficacy 5- to 9- yr-olds Vaccine efficacy
Year Method of diagnosis (N) (%)a (N) (%)a
1993 Microbiologic 14 93 14 94
2-point serology 25 91 28 75
1-point serology 24 79 26 50
Otherb 35 96 20 90
Total 98 93 88 84
1994 Microbiologic 23 56 15 42
2-point serology 36 67 36 83
1-point serology 63 71 65 c
Otherb 37 89 29 91
Total 159 77 145 72
1995 Microbiologic 14 85 9 67
2-point serology 27 82 19 64
1-point serology 39 64 45 c
Otherb 37 53 27 67
Total 117 72 100 45
1996 Microbiologic 116 67 123 3
2-point serology 245 c 288 49
1-point serology 545 c 782 c
Otherb 290 66 355 40
Total 1196 34 1548 16
1997 Microbiologic 63 51 68 57
2-point serology 110 c 131 c
1-point serology 283 c 345 c
Otherb 244 c 260 c
Total 700 c 804 c

aEstimated vaccine effectiveness; a vaccine-coverage of 96% was used to estimate the incidence and vaccine effectiveness.
bEpidemiologic, serologic (differentiation between positive two-point serology and positive one-point serology not possible), clinical or method of diagnosis unknown.
c Vaccine effectiveness could not be estimated as the percentage vaccinated was more than 96%.

Main Article

1Vaccine effectiveness = 1 – (proportion of vaccinated cases/1 – proportion of vaccinated cases) X (1 – proportion vaccinated in the population/proportion vaccinated in the population).

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