A single dose of the bivalent human papillomavirus vaccine may offer a similar level of protection against HPV-16 and 18 infections, according to research combining data from two large trials.
The findings, published in The Lancet Oncology journal, suggest that reducing the number of doses could reduce vaccine and administration costs.
The bivalent vaccine Cervarix targets HPV types 16 and 18, which are responsible for about 70% of cervical cancers.
The 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.
“It could reduce vaccination and administration costs as well as improve uptake”
Due to the lack of efficacy data on fewer than three doses, the researchers analysed existing data from two trials – the Costa Rica HPV Vaccine Trial (CVT) and the Papilloma Trial against Cancer in Young Adults (PATRICIA) trial.
The CVT included 7,466 healthy women aged 18-25 years old, while the PATRICIA trial involved 18,644 healthy women aged 15-25 years from the Asia-Pacific region, Europe, and both North and South America.
Women in both trials were randomly assigned to receive the HPV vaccine or a control, given in three doses. However, some of the women received fewer than three doses, mainly because their vaccination was discontinued due to pregnancy.
The researchers 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 infections of HPV-16 and 18, regardless of the number of doses received, said the study authors.
The same 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 the results were also relevant to girls in the recommended age range for HPV vaccination of 11-12 years.
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.
Study co-lead author Dr Aimée Kreimer, from the US National Cancer Institute, said: “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.
“If one dose is sufficient, it could reduce vaccination and administration costs as well as improve uptake,” she said.
Dr Cosette Wheeler, co-lead author from the University of New Mexico in Albuquerque, added: “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.”
An alternative bivalent vaccine, Gardasil, is used in the national NHS cervical cancer vaccination programme.