Table 3.

Estimated vaccine efficacy against 12-month incident persistent infection for women who received one, two, and three doses of a HPV vaccine compared with a control vaccine

Doses, No.	Arm	Women, No.	Events, No.	Proportion of women with incident, 12-month persistent HPV16 or HPV18 infections, % (95% CI)*	HPV vaccine efficacy, % (95% CI)*	Efficacy relative to three-dose regimen, % (95% CI)*
3 (standard regimen)†	Control	3010	133	4.4% (3.7% to 5.2%)	80.9% (71.1% to 87.7%)	Referent
	HPV	2957	25	0.85% (0.56% to 1.2%)
2‡	Control	380	17	4.5% (2.7% to 6.9%)	84.1% (50.2% to 96.3%)	104% (69.3% to 129%)
	HPV	422	3	0.71% (0.18% to 1.9%)
1	Control	188	10	5.3% (2.7% to 9.3%)	100% (66.5% to 100%)	124%§
	HPV	196	0	0.0% (0.0% to 1.5%)

^*Human papillomavirus = HPV; 95% CI = 95% confidence interval.

^†The distribution of the time at diagnosis of the case patients in the HPV and control arms was qualitatively assessed to determine whether the protection afforded by two doses may be short lived compared with that of three doses. Twenty (80.0%) of 25 breakthrough 1-year persistent HPV infections in the vaccine arm were first detected in the first year of follow-up (suggesting missed prevalent infections at enrollment) compared with 40 (30.1%) of 133 infections detected in the control arm. Sixteen (64.0%) of 25 breakthrough infections occurred among women who were HPV16 seropositive at enrollment.

^‡One of the three breakthrough infections was detected in each of the first 3 years of the study compared with 0%, 64.7%, 23.5%, and 11.8% of the 17 infections in years 1, 2, 3, and 4 of the study, respectively. One (33.3%) of the three breakthrough infections occurred in a woman who was HPV16 seropositive at enrollment.

^§No bootstrap confidence interval could be estimated due to the presence of zero events in the HPV arm after one dose of vaccine.