Single HPV vaccine dose could be as effective against infection as multiple doses
A single dose of Cervarix - a vaccine against two types of the human papillomavirus (HPV) - could be as effective in preventing infections as multiple doses, according to an international study.
"More studies, over longer periods of time, looking at rates of cervical cancer and pre-cancer as well as HPV infection are needed" - Sarah Williams, Cancer Research UK
The two types - HPV16 and HPV18 - are responsible for about seven out of 10 cases of cervical cancer.
The findings, published in The Lancet Oncology, combined data from two large phase 3 clinical trials of the vaccine.
They discovered that, after four years, the vaccine seemed to be effective among women on the trial who had fewer than the three doses often recommended by vaccination programmes.
Giving a single dose has the potential to reduce costs, as well as increase the number of people being vaccinated, the researchers suggest.
This could be particularly useful in less-developed regions of the world, where cervical cancer is more common and access to health care is lower.
Sarah Williams, Cancer Research UK’s health information manager, said that the findings were “promising”, but they weren’t immediately applicable to the UK.
“This study looked at the Cervarix vaccine, whereas the UK vaccination programmes use Gardasil, so we can’t be sure whether the findings apply to both vaccines.” she said.
Alongside helping to prevent cancer, Gardasil also protects against two other types of the virus, linked to genital warts.
“So more studies, over longer periods of time, looking at rates of cervical cancer and pre-cancer as well as HPV infection are needed,” she said.
“And there’s already good evidence that a two-dose vaccination schedule is effective – since September 2014 the UK HPV vaccination programme has recommended two rather than three doses of Gardasil,” she added.
Cervical cancer is the twelfth most common cancer in women in the UK, with around 3,100 women being diagnosed each year, but the fourth most common in women worldwide.
With limited data on the Cervarix vaccine’s effectiveness at lower doses, the team looked for evidence in data from two large studies.
These included data from 7,466 healthy women aged 18-25 years from the NCI Costa Rica HPV Vaccine Trial (CVT) and 18,644 healthy women aged 15-25 years from the Papilloma Trial against Cancer in Young Adults (PATRICIA) trial.
Women in both trials were given either the HPV-16/18 vaccine, or a control jab, in three doses. But some women ended up receiving fewer doses – allowing the researchers to investigate how that affected the vaccine’s performance.
They calculated how effective the vaccine was against HPV infection after three doses (22,327 women), two doses (1,185 women) and one dose (543 women) over a period of four years.
The vaccine appeared to be effective regardless of the number of doses received, yet the authors also cautioned that more studies would be needed before any for vaccine policy changes could be recommended.
“Using existing data, we showed that a single dose of [Cervarix] may be sufficient to substantially reduce cervical cancer incidence,” said Dr Cosette Wheeler, co-lead author from the University of New Mexico Health Sciences Center.
“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.”