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EFFECT OF HPV VACCINE ON PREEXISTING HPV INFECTION

group; P=.91). A total of 1671 women (825 in the HPV vaccine group and 846 in the control group; P=.61) had HPV PCR results available from the 12- month visit, including 134 women (56 in the HPV vaccine group and 78 in the control group) who did not have HPV PCR results available from the 6-month visit. Polymerase chain reaction re- sults were not available for 705 women because of missed visits (n=456) or study discontinuations (n=65), be- cause PCR results were not yet avail- able from the testing laboratory (n=87), or because the 12-month study visit had not yet been conducted at the time of this analysis (n=97).

Of the 705 women excluded, 341 (48.4% vs 0 among those included in the analysis; P.001) had missing 12- month data because of referral to col- poscopy after study entry. Conse- quently, women excluded from the 12- month analysis differed from those included with respect to factors related to colposcopy referral, such as mean age (20.9 years vs 21.4 years; P.001), mean lifetime number of sexual partners (2.9 vs 2.7; P=.002), frequency of abnor- mal cytologic findings at entry (62.8% vs 16.1%; P.001), and proportion of individuals with multiple HPV infec- tions (50.1% vs 40.2%; P.001). How- ever, these differences were nondiffer- ential by study group; the 705 women were comparable by group with re- spect to age (P=.22), lifetime number of sexual partners (P=.77), abnormal cy- tologic findings at entry (P=.93), pro- portion of participants referred for col- poscopy during follow-up (P = .50), proportion of individuals with mul- tiple infections (P=.24), and distribu- tion of HPV analysis groups (P=.10).

Different exclusions were applied for the analysis based on entry HC2 test- ing results because the intent of this spe- cific analysis was to examine vaccine ef- fects among the group of women positive for HPV by the clinically ap- proved HC2 test. Of the 5758 women with pelvic evaluations who were not referred to colposcopy at entry, 3711 (1866 in the HPV vaccine group and 1845 in the control group) were ex-

HPV Vaccine Group

Control Group

Vaccine Efficacy for Viral Clearance, % (95% CI)

47/172 (27.3) 54/123 (43.9)

61/222 (27.5) 73/159 (45.9)

−0.2 (−13.2 to 11.3) −3.7 (−28.2 to 16.1)

35/76 (46.1) 32/54 (59.3)

34/76 (44.7) 37/61 (60.7)

2.4 (−30.5 to 27.0) −3.5 (−62.0 to 33.8)

82/248 (33.4) 86/177 (48.8)

95/298 (31.6) 110/220 (49.8)

2.5 (−9.8 to 13.5) −2.0 (−24.3 to 16.3)

81/241 (33.8) 69/149 (46.5)

93/288 (32.0) 98/196 (50.0)

2.6 (−10.1 to 13.8) −7.0 (−31.7 to 13.0)

23/82 (28.0) 28/63 (44.4)

24/97 (24.7) 37/79 (46.8)

4.4 (−14.1 to 19.9) −4.5 (−41.4 to 22.8)

Table 2. Viral Clearance and Vaccine Efficacy for Viral Clearance for HPV-16 and HPV-18 by Study Group at 6 Months and 12 Months of Follow-up

No. Cleared/Total Infections (%)

a

Follow-up Time, mo

HPV-16 6

Abbreviations: CI, confidence interval; HPV, human papillomavirus. a P e r c e n t a g e s c a l c u l a t e d u s i n g g e n e r a l i z e d e s t i m a t i n g e q u a t i o n s m e t h o d a n d m a y t h e r e f o r e v a r y f r o m c r u d e p e r c e n t a g e s . b H P V - 1 6 / 1 8 i s d e f i n e d a s H P V - 1 6 a n d / o r H P V - 1 8 . cAll doses are defined as 2 doses at the 6-month follow-up and 3 doses at the 12-month follow-up.

c

12

HPV-18 6

HPV-16/18 (restricted to women with single infections at entry) 6

12

HPV-16/18 (restricted to women who received all vaccine doses)

6 12

12 HPV-16/18 6 12

b

cluded because they were HC2- negative, 181 (92 in the HPV vaccine group and 89 in the control group) were excluded because they were missing HC2 results from entry, and 104 (59 in the HPV vaccine group and 45 in the control group) were excluded be- cause they were had positive HC2 re- sults but negative PCR results.

A total of 1762 (874 in the HPV vac- cine group and 888 in the control group) were positive for HPV DNA by both HC2 and PCR testing. The final group for this analysis consisted of 1520 of these 1762 women for whom HPV testing results were available from the 6-month visit (752 in the HPV vaccine group and 768 in the control group; P=.68). A total of 1169 of these women (574 in the HPV vaccine group and 595 in the control group; P=.54) also had HPV PCR re- sults available from the 12-month follow- up, including 101 women (43 in the HPV vaccine group and 58 in the control group) who did not have HPV PCR re- sults available from the 6-month visit. The data freeze dates for the various com- ponents of the trial data were as fol- lows: clinical database, March 29, 2007;

risk factor questionnaire, June 26, 2006; HPV PCR database, April 25, 2007; and HPV-16/18 serology database, July 17, 2006.

Characteristics of participants in- cluded in this analysis were compared between groups. Results are summa- rized in TABLE 1. The 1088 partici- pants in the HPV vaccine group and 1101 participants in the control group were comparable with respect to age at entry, lifetime number of sexual part- ners, cytologic findings at entry, pro- portion of participants referred to col- poscopic evaluation during follow- up, proportion of individuals with multiple infections, and distribution of HPV analysis groups. The number of doses received and intervals between entry and the 1-month, 6-month, and 12-month visits were also comparable across groups (Table 1).

HPV Viral Clearance

Rates of viral clearance at the 6-month and 12-month visits and VEVC esti- mates for HPV-16, HPV-18, and HPV- 16/18 combined are presented in TABLE 2. At the 6-month visit, rates of

©2007 American Medical Association. All rights reserved.

(Reprinted) JAMA, August 15, 2007—Vol 298, No. 7

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