Cervical Cancer Vaccine May Work at Just One Dose

Issue 26 Winter/Spring 2016


Data from pair of studies suggests single shot of Cervarix® may shield against strains that cause 70 percent of tumors

The cervical cancer vaccine Cervarix® can shield against the human papillomavirus (HPV), but current recommendations mandate that it be delivered in three doses over a six-month period.

However, a new analysis of data from two trials suggests that at two doses, or even one dose, the vaccine still shields women from the two HPV strains tied to 70 percent of cervical cancers – HPV 16 and 18.

A one-dose vaccine would be hugely advantageous, experts say, especially in low-resource countries where cervical cancer remains a major killer.

“If one dose is sufficient, it could reduce vaccination and administration costs, as well as improve uptake,” study co-lead author Dr. Aimée Kreimer, of the U.S. National Cancer Institute, said in a news release from the journal The Lancet Oncology. “This is especially important in less developed regions of the world where more than 80 percent of cervical cancer cases occur,” she added.

The research, published in the journal in June, looked at combined data from two studies. One, funded by the NCI, was conducted in Costa Rica and included almost 7,500 healthy women aged 18 to 25. The other, funded by the maker of Cervarix®, GlaxoSmithKline, involved almost 19,000 females aged 15 to 25 from Asia-Pacific, Europe, Latin America and North America.

Most of the women got the full three-shot regimen of Cervarix®. However, some got fewer shots, for various reasons – for example, they became pregnant over the course of the trial.

All participants were followed for four years.

Crunching the numbers, Kreimer’s team found that women seemed to gain protection against HPV 16 and 18 regardless of how many doses they received.

There was a bonus to getting three or at least two shots of the vaccine: Women who did so often gained broader protection against strains of HPV not even targeted by Cervarix®.

However, since HPV 16 and 18 are by far the leading causes of cervical tumors worldwide, even one dose of Cervarix® could give millions of girls worldwide effective protection against cervical cancer, experts said.

Speaking in a commentary published in the journal, Dr. Julia Brotherton from the Victorian Cytology Service Registries in Melbourne, Australia, noted that, “data from studies have shown how effective one-vaccine dose campaigns can be, even in the most resource-poor settings.”

Such a campaign, “could happen every 5-10 years with the aim of vaccination of, for example, all 9-14 year old girls with one dose of the HPV vaccine,” she explained. “This campaign would not need ongoing resources to sustain annual vaccination programs against HPV in settings with many pressing health priorities and small numbers of health-care workers.”

Of course, other HPV vaccines, most notably Gardasil®, have also been approved. Kreimer’s team says their study couldn’t determine whether one dose of other HPV vaccines might offer similar protection. And they say more data is needed before current recommendations for a three-dose regimen are changed.

According to study co-author Dr. Cosette Wheeler of the University of New Mexico Health Sciences Center in Albuquerque, “a new randomized 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 4 years.”