Immunity to four strains of human papillomavirus from the quadrivalent vaccine lasted in most cases at least 8 years, according to a new study.
The vaccine covers the HPV strains 6, 11, 16, and 18.
"Three doses of HPV4 vaccine provided high protection against disease and persistent infection," Dr. Daron Ferris of Georgia Regents University, Augusta, and his colleagues reported online Aug. 18 (Pediatrics 2014;134:e657-65).
Among 1,661 girls and boys aged 9-15 years, two-thirds (1,179) were assigned to receive the quadrivalent vaccine at the start of the study, with additional doses 2 and 6 months later. The other "catch-up" group (482) received a saline placebo at those times and then, 30 months after the start of the study, received the same three-dose series of the vaccine.
Eight years after the study began, the anti-HPV immune response remained high for all four strains in both groups, although the geometric mean titers at 8 years were approximately 11-34 times lower than those at 7 months into the study.
During follow-up, no cases of HPV-related disease and four cases of HPV-related infection lasting longer than 1 year occurred in the early-vaccination group – 2 each among the females and the males. In the catch-up group, one case of disease and six cases of infection occurred among the females, and one infection occurred among the males.
The researchers observed no serious adverse events related to the vaccine during follow-up except one case of Bell’s palsy that fully resolved after 2.7 weeks.
The research was funded by Merck. Dr. Sings, Dr. Shou, Dr. Saah, and Mr. Sausser are Merck employees and stock/stock options holders. Dr. Ferris, Dr. Block, Dr. Mehlsen, Dr. Chatterjee, and Dr. Iversen have received grant funding, consulting fees, and/or speaker fees from, and/or have served on advisory boards for Merck, and Dr. Chatterjee and Dr. Iversen, for GlaxoSmithKline. The remaining authors had no financial disclosures.