Studies of two-dose and three-dose 9-valent human papillomavirus (HPV) vaccines in youth aged 9-14 years and in those up to age 26 found the vaccines to be “generally well tolerated in all vaccination groups,” according to a report at a meeting of the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices.

There were no vaccine-related severe adverse events, deaths, or discontinuations due to an adverse event.

The key points for ACIP to consider were the time interval between the first and second vaccine doses, the duration of protection provided by a two-dose regimen, and that it is imperative for patients to complete the entire series of vaccinations. A longer-term follow-up is planned, explained Dr. Alain Luxembourg, who spoke about the studies on behalf of Merck. “9-valent [vaccine] has now been licensed in more than 30 countries, [and] the ACIP recommended gardasil-9 for vaccination in 2015, so we continue to look at further developments in terms of licensure and recommendations,” he said.

The first of two 9vHPV two-dose studies was an open-label trial that examined five cohorts of 300 children; cohorts 1-3 and 5 were of children ages 9-14 years, and cohort 4 – the control – was of children and adults aged 16-26 years. All individuals in cohorts 1, 4, and 5 were female, all children in cohort 2 were male, and cohort 3 comprised males and females.

Children in cohorts 1 and 2 were put on dosing regimens lasting either 0 or 6 months. Children in cohort 3 were placed in regimens lasting either 0 or 12 months, while those in cohorts 4 and 5 were in regimens of either 0, 2, or 6 months. Vaccine administration was done over two or three visits, within a 4-week window of month 6 and month 12; those who were on a 2-month regimen were vaccinated within 3 weeks of reaching 2 months. In addition, one dose of 9vHPV was administered at 36 months to “assess immune memory.”

The second study was a 37-month trial that examined noninferiority of measured geometric mean titer (GMT) concentrations – the metric used for both studies to determine HPV concentration – at 1 month after last dose in both girls and boys who were on a two-dose regimen, and compared them with young women who received a three-dose regimen.

The results indicated that noninferior HPV concentrations at 1 month after administration of the final dose in both girls and boys “supports extending efficacy findings in women who received three doses to girls and boys who received two doses.” Furthermore, lower measure GMTs were found in girls who received only two doses versus three, although Dr. Luxembourg said the clinical significance of this finding is as yet unknown.

Dr. Luxembourg is an employee of Merck.