• Sven-Eric Olsson, Luisa L Villa, Ronaldo L R Costa, Carlos A Petta, Rosires P Andrade, Christian Malm, Ole-Erik Iversen, John Høye, Margareta Steinwall, Grete Riis-Johannessen, Agneta Andersson-Ellstrom, Kristina Elfgren, Geo von Krogh, Matti Lehtinen, Jorma Paavonen, Gretchen M Tamms, Katherine Giacoletti, Lisa Lupinacci, Mark T Esser, Scott C Vuocolo, Alfred J Saah, and Eliav Barr.
• Karolinska Institute at Danderyds Hospital, SE-182 88 Danderyd, Sweden. sven-eric.olsson@ds.se
• Vaccine. 2007 Jun 21; 25 (26): 4931-9.

BackgroundThe duration of protection afforded by vaccines represents a critical test of their utility as public health interventions. Some vaccines induce long-term immunity, while others require booster doses. Vaccines that induce long-term protection are usually characterized by the generation of immune memory. Recent trials of a quadrivalent (types 6, 11, 16, 18) human papillomavirus (HPV) vaccine have demonstrated high efficacy through 5 years of follow-up. We evaluated the extent to which the vaccine is able to generate HPV type-specific immune memory.MethodsA total of 552, 16-23-year-old women were enrolled in a double-blind, placebo-controlled study. At enrollment, subjects were randomized in a 1:1 ratio to receive three-dose regimens of quadrivalent HPV vaccine or placebo with 3 years' follow-up. A subset of 241 subjects (n=114 in the quadrivalent HPV vaccine group and n=127 in the placebo group) underwent 2 further years of follow-up. All extension subjects received quadrivalent HPV vaccine at month 60 to examine the extent of immune memory in response to the primary vaccination series.ResultsSerum anti-HPV levels declined post-vaccination, but reached a plateau at month 24 that remained stable through month 60. Administration of a challenge dose of vaccine induced a classic anamnestic response, with anti-HPV levels 1 week post-challenge reaching levels observed 1 month following the completion of the three-dose primary series. At 1 month post-challenge, anti-HPV responses were higher than those observed 1-month post-dose 3.DiscussionA three-dose regimen of quadrivalent HPV vaccine induces high efficacy and stable anti-HPV levels for at least 5 years. Vaccination also induces robust immune memory. These findings suggest that the efficacy of this vaccine will be long lasting.

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