HPV Vaccine Does Not Increase Sexual Activity

October 15, 2012 — Girls who received the human papilloma virus (HPV) vaccine at 11 or 12 years of age were no more likely to engage in sexual behavior than girls who did not receive the vaccine, according to a retrospective cohort study of longitudinal electronic data collected from a large managed care organization.

Robert A. Bednarczyk, PhD, a clinical investigator at the Center for Health Research-Southeast, Kaiser Permanente, and an epidemiologist at Rollins School of Public Health at Emory University in Atlanta, Georgia, and colleagues published their findings online October 15 and in the November issue of Pediatrics.

"We sought to test the hypothesis of a clinically meaningful increase (alternative hypothesis incidence rate ratio [IRR] of 1.5) in rates of testing or diagnosis for pregnancy or [sexually transmitted infections] or physician counseling on contraceptives after receipt of HPV vaccine in this age range," the authors write.

There were 1398 girls in the analysis cohort; almost all received the tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis adsorbed vaccine (93%) or the quadrivalent meningococcal conjugate vaccine (91%), but only 35% began the HPV vaccine series. Of those girls, 493 were exposed to the HPV vaccine and 905 were not exposed. Almost all (474/493) of the girls who were exposed to the HPV vaccine also received 1 or more of the comparison vaccines.

HPV vaccine–exposed girls were older at the time of the vaccination of interest than unexposed girls (11.9 years vs 11.6 years, respectively; P < .001). The number of all-cause medical encounters in the previous year was higher in the HPV vaccine–exposed girls than in the HPV vaccine–unexposed girls (mean, 2.6 vs 2.1; P = .024).

A total of 107 girls were tested for pregnancy and 55 were tested for Chlamydia trachomatis, but only 4 girls got pregnant and 4 girls developed C trachomatis infections.

The incidence rate of testing/diagnosis/counseling was not significantly higher in girls who received the HPV vaccine (5.5/100 person-years; adjusted IRR, 1.29; 95% confidence interval [CI], 0.92 - 1.80) compared with in girls who did not receive the HPV vaccine (3.9/100 person-years; unadjusted incidence rate difference, 1.6/100 person-years; 95% CI, −0.03 to 3.24).

The incidence rate of diagnosis-only outcomes was low for both groups (0.26/100 person-years in the HPV vaccine–exposed group compared with 0.25/100 person-years in the HPV vaccine–unexposed group; adjusted IRR, 1.11; 95% CI, 0.26 - 4.64).

The mean age at first testing/diagnosis/counseling outcome was similar for HPV vaccine–exposed girls (14.4 years) and unexposed girls (14.6 years; P = .33), and age at first diagnosis-only outcome was also similar for both groups (HPV vaccine–exposed girls, 14.8; HPV vaccine–unexposed girls, 14.6 years; P = .82).

IRRs for individual outcomes were not significantly increased in HPV vaccine–exposed girls compared with unexposed girls.

The unadjusted incidence rate difference was slightly higher for contraceptive counseling in HPV vaccine–exposed girls (0.90/100 person-years; 95% CI, 0.15 - 1.65), but there was no significant elevation in the adjusted IRR (2.31; 95% CI, 0.99 - 5.38). Adjustments were made for health-seeking behavior and for demographic traits.

Vaccination Not a "License for Sex"

"If HPV vaccination was 'a license for sex,' we would have expected to see more adverse outcomes shortly after vaccination, when the girls were more aware of their recent vaccination status," the authors write.

Alice Mark, MD, senior clinical advisor for Ipas and a member of the American Congress of Obstetricians and Gynecologists' Committee on Adolescent Healthcare, commented on the study in an email interview with Medscape Medical News.

"This study is important because it can be used to combat an important barrier to girls being vaccinated for HPV; that is, that girls might use the HPV vaccine as a license to initiate early or risky sex. Although the link between the HPV vaccine and early or risky sexual activity has not been found to be true in other studies, this study builds the evidence that the known benefit of HPV vaccination outweighs the perceived risk of early sexual activity in girls," Dr. Mark explained.

"Clinicians can use this study as an effective tool to counsel concerned parents in their practice. They can reassure parents that girls who get the vaccine are no more likely than girls who don't to engage in high-risk sexual activities," Dr. Mark concluded.

One author served as chair of the Data and Safety Monitoring Board for the study "A Post Licensure Surveillance Program for the Safety of Gardasil in a Managed Care Setting," funded by Merck Pharmaceuticals Inc, and an honoraria for this work was paid to Kaiser Permanente Georgia. Another author has conducted human papillomavirus vaccine clinical trials, with funding paid to his institution by Merck, Roche, and the National Institute of Allergy and Infectious Diseases. A third author was awarded the Maurice R. Hilleman Early-stage Career Investigator Award by the National Foundation for Infectious Diseases, which was funded by an unrestricted educational grant to the National Foundation for Infectious Diseases from Merck; however, this author had no direct interaction with Merck. The other authors and Dr. Mark have disclosed no relevant financial relationships.

Pediatrics. Published online October 15, 2012.

Fonte: www.medscape.com