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Table 1 Age-specific incidence (cases per thousand) of varicella and trends, Massachusetts, 1998–2003

From: The incidence of varicella and herpes zoster in Massachusetts as measured by the Behavioral Risk Factor Surveillance System (BRFSS) during a period of increasing varicella vaccine coverage, 1998–2003

Year Parameter Age group in years
   < 1 1–4 5–9 10–14 15–19 20+ All ages, crude
1998         
  na 144 762 1025 922 791 8241 11885
  Cases 4 66 83 23 9 34 219
  Incidence 15.2 82.6 76.4 18.6 30.2 2.2 16.5
  95% CI 4.7–49.5 59.9–113.9 55.0–104.5 10.8–32.0 8.3–109.4 1.4–3.5 12.8–21.3
1999         
  na 318 1603 1131 1094 898 8483 13527
  Cases 4 46 41 11 3 17 122
  Incidence 6.2 36.5 38.2 10.4 2.9 1.7 10.9
  95% CI 1.2–31.6 21.1–63.0 24.8–59.0 4.8–22.5 0.6–13.4 0.9–3.4 7.8–15.1
2000         
  na 139 671 790 918 693 7518 10729
  Cases 1 7 9 9 3 3 32
  Incidence 11.4 11.6 10.3 8.8 4.2 0.3 2.7
  95% CI 1.4–53.7 4.7–25.6 4.8–20.6 4.0–18.1 0.8–19.8 0.1–1.23 1.8–4.3
2002         
  na 161 600 780 831 705 7789 10866
  Cases 1 4 5 3 1 6 20
  Incidence 8.7 4.3 8.0 4.6 1.4 0.5 1.7
  95% CI 1.1–44.6 1.2–13.9 3.0–20.0 1.3–15.4 0.2–9.7 0.2–1.1 1.0–2.8
2003         
  na 155 613 827 914 726 8012 11247
  Cases 0 7 15 6 2 10 40
  Incidence 0.0 8.8 15.0 6.4 2.3 1.6 3.5
  95% CI   3.6–20.2 7.8–27.0 2.7–14.4 0.6–9.2 0.8–3.1 2.3–5.2
1998–2003         
  % change for period -100% -89% -80% -66% -92% -27% -79%
  p for trend test n.a. <0.0001 <0.0001 0.02 0.15 0.16 <0.0001
  1. a N's exclude individuals for whom age or varicella status was missing. The number excluded for these reasons was 494, 233, 478, and 195 in 1999, 2000, 2002, and 2003, respectively. Values for n's and numbers of cases are unweighted, whereas incidence rates and 95% confidence intervals are based on weighted analysis.