1. Immunogenicity in girls receiving 2 doses of the quadrivalent HPV vaccine was non-inferior to immunogenicity in young women receiving 3 doses at 7 months of follow-up.
2. The non-inferiority of the 2 doses regimen for HPV-18 in comparison to 3 doses regimen, as measured by antibody responses, did not persist at 24 months, although the clinical implications of this is not clear.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Immunogenicity for HPV-16 and HPV-18 in girls receiving 2 doses were non-inferior to women receiving the current standard 3 doses, as assessed at 7 months (titers 1 month after final dose). This shows promise for a more efficient dosing schedule, given the global burden of disease and high costs associated with the vaccine and its administration. In the future, younger girls (9-13 years old) may be able to receive 2 doses initially, in part due to their more robust immune response as compared to young women (16-26 years old). With cervical cancer being the second most common cause of cancer mortality in women, HPV control efforts could be bolstered by a reduced dosing protocol. Nonetheless, more work is needed in studying the duration of immune response and its clinical implications. In this study, non-inferiority of HPV-18 antibody protection in girls did not persist in the 2-dose group compared to the 3-dose group of girls at 24 months. Whether this reduced surrogate marker of protection has significance in propensity to contract disease, is unclear, as only a small amount of antibody should be needed at the epithelial mucosa to be effective. Studies with a larger sample and longer follow-up assessing actual disease prevalence would be needed to draw conclusions regarding the comparison of efficacy of the dosing schedules. This well-designed study may, however, guide policy perhaps in changing dosing schedule to an initial 2 doses in girls and an optional 3rd dose in adolescence. Scheduling options in other populations such as sexually active young women and men should be examined as well.
Relevant Reading: Comparison of the immunogenicity and reactogenicity of a prophylactic quadrivalent human papillomavirus (types 6, 11, 16, and 18) L1 virus-like particle vaccine in male and female adolescents and young adult women
In-Depth [randomized study]: This study examined whether 2 doses of quadrivalent HPV vaccine, given 6 months apart to girls aged 9 -13 years, resulted in immune responses noninferior to the standard 3 doses in young women aged 16-26. There were 259 girls randomized to receive 2 doses of HPV vaccine at 0 and 6 months, while 261 girls and 310 women were randomized to receive 3 doses of the same at 0, 2 and 6 months. Geometric mean Titers (GMT) ratios for HPV-16 and HPV-18 in girls receiving 2 doses were non-inferior (1.77 to 2.24 fold higher GMT) to women receiving 3 doses at 7 months. For secondary outcome of incremental protection of 3rd dose in girls, non-inferiority was demonstrated for HPV-16 and HPV-11 out to 36 months, however, HPV-18 responses at month 24 and HPV-6 at 36 months were no longer non-inferior.
By Mike Hoaglin and Rif Rahman
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