TABLE 3

Impact of qHPV Vaccination on the Risk of Cervical Dysplasia and AGWs (n = 260 493)

RDs, per 1000 Girls (95% CI)aRisk Ratio (95% CI)bNNT (95% CI)c
Dysplasia
 Program impact
  Broad−2.32 (–4.02 to –0.61)0.79 (0.66 to 0.94)431 (248 to 1639)
  Possible−1.70 (–3.08 to –0.32)0.76 (0.61 to 0.95)588 (325 to 3125)
  Probable−0.79 (–1.74–0.16)0.76 (0.56 to 1.05)1266 (575 to ∞ to NNH 6250)
 Vaccine impact
  Broad−5.70 (–9.91 to –1.50)0.56 (0.37 to 0.85)175 (101 to 667)
  Possible−4.19 (–7.59 to –0.80)0.50 (0.30 to 0.82)239 (132 to 1250)
  Probable−1.94 (–4.28 to 0.39)0.51 (0.23 to 1.12)515 (234 to ∞ to NNH 2564)
AGWs
 Program impact
  Broad−0.34 (–1.03 to 0.36)0.81 (0.52 to 1.25)2941 (971 to ∞ to NNH 2778)
  Possible−0.34 (–0.81 to 0.13)0.60 (0.31 to 1.15)2941 (1235 to ∞ to NNH 7692)
  Probable−0.29 (–0.74 to 0.16)0.63 (0.32 to 1.24)3448 (1351 to ∞ to NNH 6250)
 Vaccine impact
  Broad−0.83 (–2.54 to 0.88)0.57 (0.24 to 1.35)1205 (394 to ∞ to NNH 1136)
  Possible−0.84 (–1.99 to 0.31)0.31 (0.07 to 1.41)1190 (503 to ∞ to NNH 3226)
  Probable−0.72 (–1.82 to 0.0.38)0.34 (0.05 to 2.14)1389 (549 to ∞ to NNH 2632)
  • NNT, number needed to treat;

  • NNH, number needed to harm.

  • To address the effect of birth timing we observed, we used the entire bandwidth of data (ie, all observations in the 1992 to 1995 birth cohorts), and included birth timing as a covariate in the model. In all analyses, the birth cohorts closest to the cutoff (1993 and 1994) were weighting twice as heavily as those farthest from the cutoff (1992 and 1995).

  • a Estimated using local linear regression models.

  • b Estimated using log-binomial regression models.

  • c Reported as recommended by Altman (1998).42 When absolute RDs are not statistically significant, the limits of the CI for the NNT reflect both the possibility of benefit (NNT) and the possibility of harm (NNH). Moreover, the NNT is infinity (∞) when the absolute RD is 0. To convey the continuity of the CI, Altman42 suggests that both the NNT and the NNH be represented in 1 interval and that 0 be represented by infinity.