A single dose of the human papillomavirus (HPV) vaccine Cervarix may offer a similar level of protection against HPV infections as the current two- and three-dose schedules, according to new research published in The Lancet Oncology.
HPV infections are a leading cause of cervical cancers, which is the fourth most common cancer in women worldwide.
Cosette Wheeler, PhD, a researcher at the University of New Mexico Health Sciences Center, and Aimée Kreimer, PhD, from the National Cancer Institute (NCI), are co-lead authors of the analysis, which combines data from two large phase 3 trials.
“Our findings question the number of HPV vaccine doses truly needed to protect the majority of women against cervical cancer, and suggest that a one-dose schedule should be further evaluated," Kreimer says. "If one dose is sufficient, it could reduce vaccination and administration costs as well as improve uptake. This is especially important in less developed regions of the world where more than 80 percent of cervical cancer cases occur."
The bivalent vaccine targets HPV types 16 and 18 that are responsible for about 70 percent of cervical cancers. The HPV-16/18 vaccine was initially approved to be given in three doses over six months, but many countries are moving to a two-dose schedule in adolescents.
This new combined analysis of two independent trials strengthens previous findings from the NCI Costa Rica HPV Vaccine Trial (CVT) which reported that young women who received three, two or one dose of the bivalent vaccine were equally protected against infection with HPV-16/18 for at least four years after vaccination.
Due to the lack of efficacy data on fewer than three doses, the researchers conducted a post-hoc analysis combining data from the CVT, which included 7,466 healthy women ages 18–25 years old, and the Papilloma Trial against Cancer in Young Adults (PATRICIA) trial in 18,644 healthy women, ages 15–25, from Asia-Pacific, Europe, Latin America and North America. Women in both trials were randomly assigned to receive the HPV-16/18 vaccine or a control vaccine, given in three doses: at enrollment, one month and six months.
After excluding women with no follow up or who had cervical HPV infection at enrollment, the investigators calculated vaccine efficacy against HPV infection after three doses (22,327 women), two doses (1,185) and one dose (543). Women were followed on average for four years.
High vaccine efficacy was seen against incident HPV-16/18 infections regardless of the number of doses received. This result was also observed in a subgroup of women with no sign of HPV infection either before or at the time of first vaccination, suggesting that these results are relevant to younger girls, ages 11-12, in the recommended age range for HPV vaccination.
In further analyses, partial protection against other HPV types not included in the vaccine formulation was seen among women who received two doses six months apart, similar to that reported for three doses.
The authors caution that more data are needed before policy guidelines can be changed.
“Using existing data, we showed that a single dose of the bivalent HPV vaccine may be sufficient to substantially reduce cervical cancer incidence," Wheeler says. "Yet, a new randomised study will be needed to confirm these findings and move the field forward. Additionally, duration of protection from a single dose must be demonstrated beyond four years.”