Table 1.
Herd Effect (With 95% Confidence Interval) Against Genital Human Papillomavirus (HPV) Infection and Type-Specific HPV Prevalence (%) by HPV Vaccination Strategya in Non-HPV-Vaccinated 18.5-Year-Old Females by Trial Arm and Birth Cohort
| Arm A (Gender-Neutral) | Arm B (Girls-Only) | Arm C (Control) | ||||
|---|---|---|---|---|---|---|
| HPV Type | Birth Cohorts | Prevalence (95%CI) | HEc (95% CI) | Prevalence (95% CI) | HEc (95% CI) | Prevalencef (95% CI) |
| HPV16 | 1992–1995 | 7.5 (5.8–9.6) | 14.9 (−13.2 to 36.0) | 7.6 (6.0–9.6) | −1.3 (−29.4 to 20.7) | 8.3 (7.4–9.2) |
| 1995 | 9.5 (5.8–15.1) | −19.9 (−92.9 to 25.5) | 8.7 (5.6–13.3) | 19.2 (−81.8 to 21.9) | 8.1 (6.4–10.2) | |
| HPV18 | 1992–1995 | 5.0 (3.7–6.9) | −16.3 (−60.8 to 15.9) | 3.9 (2.8–5.4) | 15.1 (−19.8 to 39.8) | 5.0 (4.3–5.8) |
| 1995 | 1.9 (0.6–5.4) | 58.3 (−13.5 to 84.7) | 2.9 (1.3–6.2) | 27.0 (−45.8 to 63.5) | 2.7 (1.8–4.1) | |
| HPV31 | 1992–1995 | 3.5 (2.4–5.1) | 6.6 (−40.5 to 37.9) | 3.8 (2.7–5.2) | −5.9 (−51.8 to 26.2) | 3.8 (3.2–4.5) |
| 1995 | 0.6 (0.1–3.5) | 83.9 (21.2–96.7)e | 2.9 (1.3–6.2) | 34.9 (−49.0 to 71.5) | 3.4 (2.3–4.9) | |
| HPV33 | 1992–1995 | 2.9 (1.9–4.3) | −41.4 (−125 to 11.2) | 3.0 (2.0–4.3) | −86.2 (−176 to −25.5)e | 2.1 (1.7–2.7) |
| 1995 | 1.3 (0.3–4.5) | 64.9 (−57.5 to 92.2) | 1.4 (0.5–4.2) | 24.8 (−108 to 72.8) | 1.4 (0.8–2.5) | |
| HPV35 | 1992–1995 | 1.1 (0.6–2.1) | 46.1 (−17.6 to 75.3) | 1.1 (0.6–2.1) | 50.7 (−4.5 to 76.7) | 1.6 (1.3–2.1) |
| 1995 | 1.3 (0.3–4.5) | 3.4 (−203 to 69.2) | 1.4 (0.5–4.2) | 4.2 (−168 to 65.8) | 2.1 (1.3–3.3) | |
| HPV45 | 1992–1995 | 3.0 (2.0–4.5) | −36.2 (−110 to 11.8) | 2.2 (1.4–3.3) | −4.5 (−63.9 to 33.4) | 2.5 (2.0–3.1) |
| 1995 | 2.5 (1.0–6.3) | −14.5d (−178 to 52.7) | 1.0 (0.3–3.5) | 52.1d (−49.8 to 84.7) | 2.1 (1.3–3.4) | |
| HPV18/31/33 | 1992–1995 | 10.1 (8.1–12.5) | −39.6 (−71.9 to −13.4)e | 9.5 (7.8–11.7) | −6.4 (−32.4 to 14.4) | 9.8 (8.9–10.9) |
| 1995 | 3.8 (1.8–8.0)b | 59.1 (14.3–80.5)e | 6.8 (4.1–11.0) | 23.9 (−23.2 to 53.0) | 6.7 (5.2–8.7) |
Abbreviations: CI, confidence interval, HE, herd effect.
aArm A, gender-neutral (49% girls, 23% boys HPV-vaccinated); Arm B, girls-only (47% girls HPV-vaccinated); Arm C, hepatitis B virus (HBV) vaccination.
bSignificantly different.
cGeneralized estimating equation (GEE) estimates adjusted for Chlamydia trachomatis/mobility/smoking/vaccination coverage, balanced for equal proportions of HBV vaccinated and nonvaccinated. Herd effect (1-ratio of risks, GEE model, HBV-vaccinated/unvaccinated-ratio balanced between arms using mean GEE estimates from 21 balanced materials).
dNot adjusted for mobility.
eSignificant.
fThe prevalence in Arm C is mean of prevalence estimates from 21 balanced materials. For the estimation of pertinent 95% CI, a material with the mean prevalence and actual size of Arm C was used.