A major new study has found that a single dose of the human papillomavirus vaccine, Cervarix, is just as effective as the currently recommended three doses when it comes to protecting against two high risk, cancer-causing strains of the virus.
What's more, a special two-shot protocol could protect against additional strains of the virus not previously thought to be addressed by the vaccine.
The Background
Cervical cancer is the fourth most common cancer for women across the globe, and by 2020, it’s estimated that oropharyngeal cancer -- which is found in the back of the throat and affects both men and women -- will be the most common HPV-related cancer in the world.
A vaccine for these diseases is available in the form of the HPV vaccine, but not very many people are getting it. While you might think that people would be lined up around the block to get shots that can prevent genital warts as well as cancer in the cervix, anus, vagina, penis and the back of the throat, the rates of vaccination in the U.S. have been disappointingly low ever since the vaccine debuted in 2006.
The Setup
For this new study, researchers behind two large landmark HPV vaccine trials got together to combine the data on a total of 26,110 female participants who had been randomized to receive either three shots of the HPV vaccine Cervarix, which was approved for girls and women in 2009, or control injections.
For a number of life reasons, like pregnancy, some women stopped at just one or two HPV vaccine shots and couldn’t complete the series of three. Investigators like Dr. Cosette Wheeler, who studies HPV at the University of New Mexico Health Sciences Center, wanted to look back at the data after the trial was done to see how well just a single shot of the vaccine protected this small group of women against HPV.
The Findings
Wheeler and her partners found that just a single shot of the Cervarix HPV vaccine protected the women for at least four years against the two virus strains, known as 16 and 18, that cause 70 percent of cervical cancer. This level of protection was similar to the protection people got after two and three shots.
In an intriguing twist, the researchers also found that women who received two Cervarix shots six months apart -- as opposed to three shots in six months -- were protected against more HPV strains than just the 16 and 18 strains the vaccine was made to address. It’s not certain yet why that is, but the results suggest that two shots could be an even more optimal schedule for Cervarix than how it’s currently prescribed.
The study was published Wednesday in the medical journal The Lancet Oncology.
The Takeaway
There are a number of reasons parents aren’t signing their kids up for the vaccines. For one, they’re recommended for children between ages 11 and 12, and it’s apparently too icky for some parents to think about giving their pre-pubescent kids a vaccine against a sexually transmitted disease. (Of course, we vaccinate infants against Hepatitis B, which is also transmitted sexually, but logic doesn't always play.)
But there is also a very practical reason parents aren’t vaccinating their kids: The HPV vaccine has to be administered in three injections over the course of six months, as approved by the Food and Drug Administration. Three shots means three visits to the doctor, and any number of transportation issues, job scheduling problems, and other barriers can get in the way of those second and third shots. The result is vaccination rates that are low and staggered.
Wheeler's results could change that. If future trials confirm her findings, that number could be reduced to two shots six months apart, or even one shot. The findings also bode well for women in developing countries, where access to vaccines is even more difficult and the need for them is even greater.
"It costs money to have people coming to get more doses of vaccine,” Wheeler told The Huffington Post. "In the developing world, where it's even more difficult than in the United States, being able to give just 1 or 2 doses would help women worldwide. That is the most significant point of the study."
The Catch
Wheeler hopes that people in the U.S. don’t start taking the results of her trial as a justification for only showing up for one or two vaccine shots, because the trials tested only Cervarix.
“In the U.S., the HPV vaccine most widely used is Gardasil, made by Merck,” Wheeler explained. "Our studies were with Cervarix, and we do not know whether the two-dose and the spacing apart [observation] or the one dose observation will be upheld with Gardasil. So people may get the wrong message without knowing that."
To combat this, Wheeler hopes that the results of her study spur randomized controlled trials for both Cervarix and Gardasil to confirm her one-shot and two-shot data. That way, public health officials might one day be able to come up with a new vaccine schedule that requires fewer shots while still providing the maximum amount of protection. Of course, this also depends on whether just one or two doses of the vaccine can protect against HPV for up to 10 years, the way that the current three-dose schedule does.
Dr. Lois Ramondetta, a gynecological oncologist at The University of Texas MD Anderson Cancer Center and chief of gynecologic oncology at Lyndon B. Johnson General Hospital, wasn’t part of the study but agrees with Wheeler’s caveats. While Ramondetta praised the study’s analysis and design, she said it was important to remember that Cervarix was made to combat only two HPV strains, while the competing brand Gardasil was initially approved in 2006 for four strains, and most recently nine strains late last year. Still, she was grateful for the new data and said that any new information that could help protect people against cancer was welcome.
"I spend 100 percent of my time taking care of uninsured people with high risks of HPV-related diseases, and I want to see us vaccinate everybody,” Ramondetta said. “The more data we get supporting the use of an HPV vaccine, the better.”