There's a surprising advantage to a vaccine that protects against the most common sexually transmitted infection in the US

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A vaccine that protects against the most common sexually transmitted infection in the US has had a hard time catching on.

HPV, or human papillomavirus, is the most common sexually transmitted infection in the US, according to the CDC. It's responsible for nearly all cases of cervical cancer, of which there are about 12,000 new cases in the US every year. Having an effective vaccine rollout is critical to reducing this prevalence, and researchers think they've come up with the most cost-effective model that will end up saving the US healthcare system more money in the long run, even though it requires a newer, more expensive vaccine.

The first HPV vaccine was approved in 2006, and shortly after, the CDC started recommending that all girls ages 11 and 12 receive the vaccine. In 2010 the CDC gave the OK for boys of those ages to start receiving the vaccine as well. A newer version of the vaccine was approved in 2014 called Gardasil 9 that covers even more HPV serotypes, or variation within a virus. Gardasil 9 decreases cancer incidence by 73% (compared to the 63% reduction by the 2- and 4-serotype versions), while it decreases mortality by 49% (compared to 43%).

And a new study published Monday in the Proceedings of the National Academy of Science suggests that using the vaccine that covers the most types of HPV will be a cost-effective way to prevent future cases of cervical cancer, even though it comes in at a higher cost per dose.

The new vaccine costs about $13 more than the vaccines for the 4 strains and $18 more than the the vaccines for the 2 strains, the researchers from Yale University and the University of Waterloo estimated. Even so, they projected that using the Gardasil 9 vaccine vaccine instead of the other versions would actually come out at about the same cost if not lower in the long run. 

The existing number of people who are currently being vaccinated under each state's program varies significantly depending on the state. 

And the researchers found that the cost of treating HPV and cervical cancer would be roughly the same when using Gardasil 9 versus the 2- and 4-strain vaccines if we were to keep vaccinating as many people as we do right now every year. But, if we amped it up where more people were getting vaccinated, it would cost $2.7 billion more to do the 2- and 4-serotype versions than the 9-serotype version.

That's because the lower incidence of cancer and death would cut down on costs that would be absorbed by the higher cost of the vaccine. So in the end, that extra $13 or $18 per dose would be far less expensive than the cost of treating HPV or cervical cancer.

To come to that conclusion, the researchers had to look at HPV infection, cervical cancer, vaccination, and interstate migration rates for each of the 50 states and DC, breaking it down by age group. HPV vaccination policies vary widely between states, with only Virginia and Rhode Island as well as DC have some form of requirement for school-aged kids to be vaccinated. In comparison, other vaccines like chickenpox are required in a majority of states. 

According to CDC data, less than half of girls and even fewer boys had completed the three-dose series of shots in 2013. Because the vaccine is for an STI, parents tend to worry that if their kids get the vaccine, they'll feel as if it's acceptable to have sex. Others have expressed concern over the safety of taking the vaccine, though those have largely been reviewed and disproven.

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