Two doses of the quadrivalent HPV vaccine in girls may be as effective as three in young women, say researchers.
The Canadian researchers observed 520 girls aged 9 to 13 years old, who were randomised to receive either two or three doses of the quadrivalent HPV vaccine, and 310 young women, aged 16 to 26 years old, who received the standard three-doses of the HPV vaccine. Antibody levels were measured at 0, 7, 18, 24, and 36 months.
Mean antibody levels in girls receiving two doses were 7,344 mMU/mL for HPV-16 and 1,169 mMU/mL for HPV-18. This was compared with levels of 3,545 mMU/mL for HPV-16 and 664 mMU/mL for HPV 18 in those receiving three doses. The GMT ratios were non-inferior for girls who received two doses versus young women who received three doses: 2.07 for HPV-16 and 1.76 for HPV-18. The immunogenic response in girls was noninferior after two doses versus three doses of the quadrivalent HPV vaccine by month 7; however, the evidence for noninferiority disappeared for HPV-18 by month 24 and for HPV-16 by month 36.
What does this mean for GPs?
The authors observed: ‘The clinically meaningful difference between the two- and three-dose schedules for girls cannot yet be determined’ and concluded: ‘Among girls who received 2 doses of HPV vaccine six months apart, responses to HPV-16 and HPV-18 one month after the last dose were non-inferior to those among young women who received three doses of the vaccine within six months. Because of the loss of noninferiority to some genotypes at 24 to 36 months in girls given two doses versus three doses, more data on the duration of protection are needed before reduced-dose schedules can be recommended.’ The study was not sponsored by the HPV vaccine manufacturer.