The HPV vaccine provides effective protection from the human papilloma virus and the cancers it can induce. Because HPV is transmitted sexually, inclusion in mandatory vaccination schedules has been a controversial issue, and legislation varies by state. Complicating matters further, companies have continued to improve the vaccine, expanding the list of viral strains that it protects against. A new study in PNAS finds that having states require the latest, most protective HPV vaccine for girls and boys would be highly cost-effective and would lead to better health outcomes at the national level.

HPV is the most prevalent sexually transmitted infection in the US, with over 100 viral strains circulating in the population. Over half of cervical cancer cases in the US are thought to be caused by HPV, which can also cause vaginal cancer, penile cancer, anal cancer, and cancers of the mouth and throat.

Fortunately, several vaccines for HPV are now available, including bivalent, quadrivalent, and nonavalent—these protect against two, four, and nine strains of HPV respectively. These vaccines can protect women from 66-81 percent of cervical cancers, depending on the number of strains that are included in the formulation.

Since states have drastically different recommendations regarding HPV vaccination, it can be challenging to analyze vaccination rates and the cost/benefit ratio. Migration across state lines is also common, particularly in the years between vaccination, which occurs in adolescence, and disease onset, which occurs in early adulthood.

To study HPV vaccination and cervical cancer rates, a team of researchers developed a complex statistical model that took into account HPV infection, cervical cancer rates, vaccination rates, and interstate migration for all 50 states and Washington DC. To approximate sexual mixing and interactions, the researchers used data on rates of partnership formation from the National Survey for Family Growth. Additionally, they used a comparison of state-specific adolescent rates of vaccination to determine the cost effectiveness of new programs.

The researchers found that the 9-strain HPV vaccine would be considerably more effective in preventing cervical cancer cases and deaths than either of the less thorough versions. Based on their statistical analysis, they conclude that switching to the nonavalent HPV vaccine would have the same public health and economic benefit as raising the rates of vaccination by eleven percent but would cost almost three billion dollars less.

If all states switch to the nonavalent HPV vaccine, then the state-specific health savings per capita could be as high as four dollars and forty cents. Additionally, all states (not just those with vaccination programs) would see a considerable increase in residents’ quality adjusted life years (QALYs). QALYs are a standard measure of effectiveness for public health interventions, assessing the number of additional high-quality years of life that an intervention provides.

The statistical analysis also showed that we’d see greater benefits from increasing vaccination rates in states that currently have lower rates compared to increasing rates in states that already vaccinate the majority of adolescents, due to the increase in herd immunity for states that currently have low vaccination rates.

Since interstate migration is likely to occur in the years between vaccination and onset of cancer, the researchers argue that a nationally funded HPV vaccination campaign is likely to have the biggest impact. A big fraction of the health and economic benefit of HPV vaccination will happen outside a state’s borders, and this migration reduces states’ motivation to invest heavily in an HPV vaccination program. So federal involvement may be needed to see the maximum public health and economic benefit.

The researchers write that a cohesive national vaccination plan using the nine-strain HPV vaccine would provide the maximum economic and health benefits while limiting costs. However, this could prove to be a controversial recommendation, because some groups may find a federally-orchestrated vaccination schedule for a sexually transmitted virus to be inappropriate.

Regardless of how it’s arranged, teens within the vaccination window should be vaccinated with the nonavalent HPV vaccine before they are too old for vaccination—girls should be vaccinated by age 26, and boys (with some exceptions) should be vaccinated by age 21, according to CDC recommendations.

PNAS, 2016. DOI: 10.1073/pnas.1515528113 (About DOIs).