Girls who receive a two-dose regimen of human papillomavirus (HPV)–16/18 AS04-adjuvanted vaccine at any age between 9 and 14 years, in either a 6-month or a 12-month interval, appear to be equally protected as those who received a 6-month, three-dose regimen at the age of 15-25 years, according to a new study.

“The licensed vaccines HPV-16/18 AS04–adjuvanted (Cervarix; GSK Vaccines) and HPV-6/11/16/18 (Gardasil; Merck) were first approved as regimen including three doses (3D) with administration over a 6-month period,” reported Thanyawee Puthanakit, MD , of Chulalongkorn University in Bangkok, and her associates. “Reduced dose schedules could make vaccination easier to implement and more affordable, creating the potential for higher vaccination coverage and improved cervical cancer protection.”

The investigators enrolled girls aged 9-25 years starting in June 2011, from 33 clinical sites in Canada, Germany, Italy, Taiwan, and Thailand. The study lasted through January 2013, during which time 1,447 girls were enrolled and 1,428 were randomized into one of three cohorts: one receiving the two-dose, 6-month regimen; one receiving the two-dose, 12-month regime; and one receiving the three-dose, 6-month regimen. In the former two cohorts, girls aged 9-14 years would receive their doses at 0 months and either 6 or 12 months, depending on the cohort. In the three-dose regimen, girls aged 15-25 years received doses at 0, 1, and 6 months. At enrollment, 550 girls were randomized into the two-dose, 6-month regimen; 415 girls into the two-dose, 12-month regimen; and 482 girls into the three-dose, 6-month regimen. Follow-up occurred at 1 month after they received the final dose for all three cohorts.

Ultimately, 534 girls in the two-dose, 6-month cohort; 394 in the two-dose, 12-month cohort; and 427 in the three-dose, 6-month cohort completed the study through the 1-month follow-up. Serologic testing indicated that girls in both the two-dose cohorts were not immunologically worse off than those who were in the three-dose cohort, with seroconversion differences of 0.00 when comparing HPV-16 and HPV-18 antibodies between any two of the three regimens. Furthermore, geometric mean antibody titer ratios for HPV-16 and HPV-18 were 1.09 (95% confidence interval, 0.97-1.22) and 0.85 (95% CI, 0.76-0.95) for the 6-month two-dose regimen vs. three-dose, and 0.89 (95% CI, 0.79-1.01) and 0.75 (95% CI, 0.67-0.85) for 12-month two-dose regimen vs.three-dose, indicating little statistically significant difference.

“The flexibility around the timing of the second dose, giving the option of annual vaccination over 2 consecutive years, is an added benefit [because] reduced dose schedules of HPV vaccines may facilitate vaccination implementation and reduce cost, allowing for higher vaccination coverage and potentially more girls being protected from cervical cancer,” the investigators noted.

The study was supported by GlaxoSmithKline Biologicals SA. Dr. Puthanakit received a grant from GSK through her institution. Some of her many coauthors disclosed relationships with GSK and/or other pharmaceutical companies.


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