The newest HPV vaccine has the potential to safely and effectively prevent at least four different kinds of cancer in the population recommended to receive it, based on findings in a study in Pediatrics today. Gardasil 9, manufactured by Merck, protects against nine strains of the human papillomavirus, an infection transmitted through direct or indirect contact with the genitals of an infected person.
Individuals infected with these strains can expect their infection go away on its own approximately 90 percent of the time, but infections that do not resolve on their own can develop into cervical and other cancers. Researchers and public health officials expect that prevention against these HPV strains with the vaccine will translate into reduced cancer incidence, though the vaccine has not been available long enough to confirm this.
Researchers tested the vaccine in preteens and teens, those that the CDC’s Advisory Committee on Immunization Practices recommends receive the vaccine, to ensure the vaccine works at least as well as it did in those in earlier clinical trials. The verdict? It seems to work even better, given the stronger antibody response in the recipients.
“With little kids, preteens and teens, you have to show that the antibodies are as good or better than in adult women, whom we know efficacy data in,” said Dr. Stanley Block, a pediatrician in Bardstown, Kentucky, and a co-author of the study, which was funded by Merck. “This vaccine is critically important because we’re talking about four cancers we know absolutely for sure that it prevents – cervical, vulvar, anal and vaginal – and about two thirds of all oral cancers that it should prevent.”
In the study, researchers gave 3,066 boys and girls, ages 9 to 15, a three-dose series of the HPV-9 vaccine. The second dose was administered a month after the first, and the third dose at six months later. A month after the third dose, more than 99% of the participants had sufficient antibody levels for all nine strains included in the vaccine.
At a follow-up two and a half years later, the participants’ antibody levels were still going strong, with no reason to suspect they will wane. If immunity from the vaccine does wane, a booster might be considered to maintain sufficient immunity to prevent contracting an HPV strain that could develop into cancer. Women who have received the vaccine should continue to follow recommendations for regular cervical cancer screenings to detect precancerous cells.
“Studies for the quadrivalent [four-strain] and bivalent [two-strain] vaccine have followed study participants for about eight to ten years to date and have found no evidence of waning protection,” said Dr. Lauri Markowitz, of the Division of STD Prevention at the CDC, who was not involved in this study.
The most current study on the duration of Gardasil’s effectiveness, published last year, shows that the vaccine continues to be effective eight years after the last dose, though that study had a high level of drop-outs from participants. Block, who coauthored that study as well, said new data not yet published will show that the protection continues beyond eight years.
Gardasil 9 protects against HPV types 6, 11, 16, 18, 31, 33, 45, 52 and 58. While HPV-16 and HPV-18 are responsible for the lion’s share of cancer, the combination of all these strains are expected to prevent 90% of all the cancers that can be caused by HPV, Block said. That means avoiding more than 200,000 cases of precancerous lesions – which require various invasive procedures to remove – and about 23,000 cases of cancer that lead to death, metastatic disease, surgeries and/or chemotherapy, he said.
“The implications of this vaccine are tremendous,” Block said. “This is preventing huge numbers of biopsies, LEEPs and cone biopsies. We’re preventing the ultimate thing, which is the treatments.”
A LEEP, or loop electrosurgical excision procedure, basically burns off precancerous lesions that can develop into cervical cancer if not treated. Cone biopsies are an invasive method used to diagnose precancerous or cancerous cells. Some of these interventions may increase the risk of infertility.
The risks of the vaccine, on the other hand, are minimal. Minor reactions can include pain, redness and swelling at the injection site, a mild fever, headache and fainting. These are the most common reactions, and more serious reactions can include more serious or longer lasting headache or fever.
“Sitting or lying down for about 15 minutes after a vaccination can help prevent fainting and injuries caused by falls,” Markowitz said. The most serious adverse event that can occur from Gardasil 9 is a severe allergic reaction, called an anaphylactic reaction, she said. These can occur about once per one million vaccinations.
“To avoid anaphylaxis, people who are allergic to certain ingredients of the vaccine should not get vaccinated,” Markowitz said. “People who are allergic to yeast should not get Gardasil 9 or Gardasil, and people who are allergic to latex should not get Cervarix.” Cervarix is the bivalent vaccine manufactured by GlaxoSmithKline. No other serious reactions have been found to be caused by either vaccine.
Although a range of other concerns have been reported following the HPV vaccine, a thorough review of the evidence by the Institute of Medicine and multiple studies since then have found no evidence that any other conditions reported were caused by the vaccine. All conditions that happened occurred at the same rate in those who did not receive the vaccine as those who did.
“When you go head to head with people who got the vaccine and people who don’t in post-marketing studies, you find there’s no difference in rates of anything at all in the vaccine versus non-vaccine groups,” Block said.
That basically means that those who don’t have the above listed allergies have no reason not to follow the CDC recommendations for all preteens to receive the vaccine. If a person has already received three doses of the quadrivalent HPV vaccine (the original Gardasil), however, there is no reason to get Gardasil 9 unless they are in a high risk group for contracting the virus, Block said.
High risk individuals includes those who have unprotected sex, especially with multiple partners. All women receiving either vaccine should also continue to get the recommended cervical cancer screenings.
For those who have not received any HPV vaccines, Block recommends they receive one dose of quadrivalent Gardasil, which needs to be used up, followed by second and third doses of Gardasil 9.
“I find it more prudent to try to protect those [who have already received one dose of Gardasil] with the HPV 9,” Block said. “We have four cancers we know this vaccine is going to prevent and one cancer we know it should prevent. You’re preventing five cancers for your child. Do I need to say anything more?”
This post has been updated to reflect the importance of continuing to get cervical cancer screenings, and a sentence has been removed regarding the safety of Gardasil 9 following three doses of quadrivalent Gardasil because insufficient evidence exists to know the safety either way.
