EFFECT OF HPV VACCINE ON PREEXISTING HPV INFECTION
preparation to reduce the risk of car- ryover. In addition, using DNA extracted from the same aliquot, and to ensure that HPV-16 and HPV-18 infections were not missed, all speci- mens that screened positive for HPV DNA using SPF10 DNA enzyme immunoassay but were negative for HPV-16 or HPV-18 by LiPA were tested for the presence of HPV-16 and HPV-18 DNA using type-specific primers, as previously described.23,24
Enrollment specimens (prevaccina- tion) and specimens collected at the 6-month and 12-month visits were tested by the PCR method. For the en- rollment and 12-month visits, cervical specimens collected during the pelvic examination were used. For the 6-month visit, self-collected cervico- vaginal specimens were used. In addi- tion, for the subset of women who had a pelvic examination performed at the time of the 6-month visit, cervical speci- mens collected during the pelvic ex- amination were used for PCR-based HPV DNA testing.
For 672 women with both self- and clinician-collected exfoliated speci- mens at the 6-month visit, a high de- gree of concordance was observed in HPV results from these 2 specimen types. Agreement and values for HPV detection between the self-collected and clinician-collected specimens were 96.0% and =0.86 (McNemar P=.56, giving no indication of directionality) for HPV-16 and 97.6% and = 0.81 (McNemar P.99) for HPV-18. Over- all agreement (all types) was 89.4% with
=0.59 (McNemar P=.19). Given this
high level of agreement, HPV testing re- sults using the self-collected speci- mens were used to define HPV status at the 6-month visit.
HPV-16/18 Antibody Testing
An enzyme-linked immunosorbent as- say was used to test serum specimens collected from participants at entry (prevaccination) for antibodies against HPV-16 and HPV-18, using previ- ously described methods.10 Testing was performed at GSK Biologicals in Rix- ensart, Belgium.
Chlamydia trachomatis and Neisseria gonorrhoeae DNA Testing Presence of C trachomatis and N gon- orrhoeae infection was determined by testing for the presence of DNA from these pathogens in a 2-mL aliquot of exfoliated cells collected at entry (pre- vaccination) and stored in Preservcyt solution. The HC2 method was used per manufacturer’s instructions.25 Testing was performed in a laboratory located at the University of Costa Rica.
Data analyses were directed by the trial co–principal investigators (A.H. and R.H.) and the trial statistician (S.W.). The analyses were performed by pro- gramming staff at the trial’s data man- agement center (Information Manage- ment Services Inc, Silver Spring, Maryland) under direct contract and su- pervision by the National Cancer In- stitute and handled according to stan- dard operating procedures that ensure maintenance of blinding and overall trial integrity. Investigators, trial staff, and participants were unaware of in- dividual participants’ vaccine group assignment.
Comparisons between study groups with respect to general characteristics were made using the 2 test for cat- egorical variables and the Wilcoxon test for continuous variables. Among infected women, 42.6% had more than 1 HPV type at enrollment. We chose to use an infection rather than a woman as the unit of analysis because of our interest in clearance of indi- vidual HPV types.
We evaluated the following HPV cat- egories: HPV-16; HPV-18; HPV-16/18 (HPV-16 and/or HPV-18); HPV types from the alpha-9 species, excluding HPV-16 (HPV types 31, 33, 35, 52, and 58); HPV types from the alpha-7 spe- cies, excluding HPV-18 (HPV types 39, 45, 59, and 70; HPV-68 was not con- sidered in this category because LiPA cannot differentiate HPV-68 from HPV- 73); oncogenic HPV types other than those from the alpha-7 and alpha-9 spe-
cies (HPV types 51, 56, 66, and 68/ 73); and nononcogenic HPV types (HPV types 6, 11, 34, 40, 42, 43, 44, 53, 54, and 74). In addition, we evalu- ated HPV positivity by the HC2 test at entry, as evaluation of this group is rel- evant from a clinical management perspective.
Percentage clearance was evaluated independently at the 6-month visit (after 2 doses of vaccine) and at the 12-month visit (after 3 doses of vac- cine). Viral clearance of a specific HPV type was defined as failure to detect at the 6-month or 12-month visit an HPV type that was present before vaccination. For the analysis of viral clearance among women who were HC2-positive at entry, viral clearance was defined as absence at the 6-month or 12-month visits of HPV types detected at entry by type- specific PCR-based testing. Those who were positive at entry or follow-up by HC2 analysis but nega- tive for all specific types tested (ie, HC2-positive/SPF10-positive/LiPA- negative) were considered to be posi- tive for an unknown type.
Women who tested positive for an unknown type at entry and follow-up were considered to have a persistent infection (n=13 or 0.5% of all infec- tions at 6 months; n=13 or 0.7% of all infections at 12 months). Women positive at entry for an unknown type who tested positive for a known HPV type at the follow-up visit were con- sidered to have cleared their initial infection and acquired a new one (n=46 or 1.7% of all infections at 6 months; n = 31 or 1.5% of all infec- tions at 12 months). Similarly, women positive at entry for a known type who tested positive for an unknown type at the follow-up visit were considered to have cleared their initial infection and acquired a new one (n=89 or 3.3% of all infections at 6 months; n=98 or 4.9% of all infec- tions at 12 months).
Vaccine efficacy for viral clearance (VEVC), a measure of the percentage reduction (or increase) in infection rates observed when the HPV vaccine group
746 JAMA, August 15, 2007—Vol 298, No. 7 (Reprinted)
©2007 American Medical Association. All rights reserved.