Human papillomavirus (HPV) vaccines administered in 3 doses over a period of 6 months can help prevent cervical cancer but cost (almost $400 for the 3-dose regimen in the United States) may limit its use in countries with fewer resources. Findings appearing today in JAMA’s special child health theme issue suggest that 2 doses of HPV vaccine may work as well as 3 doses when given to girls aged 9 to 13 years.
Each year, about 530 000 women are diagnosed with cervical cancer, the second most common cause of cancer morbidity and mortality in women around the world, and about 275 000 women die of the disease, with 88% of deaths occurring in developing countries. Infection with certain strains of HPV plays a role in the development of cervical cancer; HPV vaccines protect against HPV genotypes 16 and 18, which account for about 70% of cervical cancer cases.
To determine the extent to which 2 doses of HPV vaccine protect against infection, in August 2007 through February 2011, Canadian researchers randomly assigned girls (9-13 years old) to receive either 3 doses of quadrivalent HPV vaccine (the second and third doses 2 months and 6 months after the first dose) or 2 doses (with the second dose 6 months after the first one). In addition, young women (16-26 years old) received 3 vaccine doses according to the same 3-dose schedule. To evaluate response to the vaccine, levels of antibodies against HPV genotypes 16 and 18 were measured at 0, 7, 18, 24, and 36 months. The researchers found that among girls who received 2 vaccine doses 6 months apart, responses were comparable with the responses among young women who received 3 doses.
Lead author Simon R. M. Dobson, MD, with British Columbia Children’s Hospital in Vancouver, spoke with news@JAMA about his team’s findings.
news@JAMA: Why did you do this study?
Dr Dobson: Even before the HPV vaccine was licensed in Canada in 2006, Canadian researchers were already meeting to raise the questions that needed to be answered regarding the best use of the vaccine, and high up on the list was, “Why 3 doses?” Because while it’s a great vaccine, it’s a very expensive vaccine. We wanted to use the vaccine most efficiently and considered 2 vs 3 doses.
news@JAMA: Why is the vaccine given in 3 doses?
Dr Dobson: It is traditional to give protein vaccines [such as the HPV vaccine] in 3 doses: 2 primers and then a final dose. But we wanted to know if the 2 priming doses were necessary or could it be done with 1 priming dose and a final dose 6 months later.
news@JAMA: Are your results strong enough to justify immunizing with only 2 doses?
Dr Dobson: No, but it’s a start. There are 2 bits of information still required. They center on the long-term duration of response of 2 doses compared with 3 doses and whether giving a booster at 60 months after initiation of vaccination is more advantageous than just 2 doses at 0 and 6 months.
news@JAMA: You mentioned the high cost of the vaccine as an impetus for your study. What is the value of 2 doses over 3 in terms of public health?
Dr Dobson: The public health question is how much protection do you need to afford adequate protection of the population? So it’s a redistribution of resources such that with the cost savings from fewer doses, you can give the vaccine to more girls for the same cost. The vaccine is very effective, but it doesn’t work in girls who don’t get it. Worldwide, if you’re in a country with little resources, especially a lack of screening programs, a reduced vaccine schedule could give protection against the cancer because then it becomes affordable.