The quadrivalent human papillomavirus (HPV) vaccine protects against the two types of HPV that have the highest risk of cancer and two types that cause genital warts. The vaccine is marketed by Merck & Co. in the US under the name Gardasil (Silgard in Europe) prevents four HPV types: HPV 16 and 18, as well as HPV 6 and 11, which cause 90% of genital warts. For a variety of reasons, some parents do not want their children to be vaccinated. Among the reasons are concerns regarding safety and effectiveness. Those concerns should be reduced by a new long-term study that was published online on August 18 in the journal Pediatrics by an international team of researchers,
The study group comprised 1,781 boys and girls aged 9 to 15 years who had never engaged in sexual intercourse. The subjects were assigned 2:1 to receive the vaccine or a saline placebo at day 1 and months 2 and 6. At month 30, the placebo group (482 subjects) were given the vaccine following the same regimen and both groups were followed through month 96. Children 16 years or older were eligible for evaluations regarding vaccine effectiveness. The primary goal was to assess the long-term effectiveness against the four types of HPV. The secondary goal was to estimate vaccine effectiveness against HPV-related persistent infection or disease.
The investigators found that for each of the HPV4 vaccine types, vaccination-induced anti-HPV response persisted through month 96. Among the 429 children who received the vaccine at an average age of 12, none developed HPV-related disease or persistent infection of 12 or more months’ duration. The attainment of new sexual partners (among those 16 years or older) was approximately1 per year. The children who received the HPV4 vaccine at month 30 (average age 15 years) had a similar baseline rate of seropositivity (indicating viral infection) to one or more of the four HPV types to those vaccinated at day 1 (average age 12 years); however, four of the nine subjects vaccinated at the later age were seropositive to three vaccine types, indicating previous HPV exposure. No new significant serious adverse events were observed for eight years post-vaccination among both genders.
The authors concluded that when the quadrivalent HPV vaccine was administered to adolescents, it was found to have durability for clinically effective protection and sustained antibody titers over years8 years.
The researchers are affiliated with: Georgia Regents University, Augusta, Georgia; Phramongkutklao Hospital, Bangkok, Thailand; Kentucky Pediatric and Adult Research, Inc., Bardstown, Kentucky; Center for Research in Population Health, National Institute of Public Health, Cuernavaca Morelos, Mexico; Clinical Research Center, Medellín, Colombia; Primary Physicians Research, Pittsburgh, Pennsylvania; Coordinating Research Centre, Frederiksberg Hospital, Frederiksberg, Denmark; University of South Dakota Sanford School of Medicine, Sanford Children’s Specialty Clinics, Sioux Falls, South Dakota; Haukeland University Hospital, Bergen, Norway; and Merck & Co., Inc., Whitehouse Station, New Jersey.