(RxWiki News) Doctors don't usually encourage patients to deviate from their vaccination schedules, but new evidence suggests that less may actually be more — at least when it comes to the HPV vaccine.
A new study found evidence that only one dose of the human papillomavirus (HPV) vaccine might be enough to prevent cervical cancer in most cases.
“If one dose is sufficient, it could reduce vaccination and administration costs as well as improve uptake," said study co-author Aimée R. Kreimer, PhD, of the National Cancer Institute (NCI), in a press release. "This is especially important in less developed regions of the world where more than 80 percent of cervical cancer cases occur."
HPVs are a group of more than 200 related viruses, named for the warts (papillomas) that some of these viruses can cause. Some HPV viruses can lead to cancer, especially cervical cancer — of which there will be an estimated 12,900 new cases in the US during 2015, reports the NCI.
More than 40 HPVs can be easily spread through direct sexual contact, from the skin and mucus membranes of infected people to the skin and mucus membranes of their partners. The most common types of HPV can be prevented with vaccines, however.
"The HPV vaccine, in my opinion, is one of the greatest advances in women's health care in the last 20 years," said Andre F. Hall, MD, an OB-GYN at Birth and Women's Care in Fayetteville, NC, in an interview with dailyRx News. "HPV is the most common sexually transmitted disease and is very common in sexually active adults."
According to Dr. Hall, HPV vaccines are given as a series of three shots over six months. There are three types of HPV vaccine (Cervarix, Gardasil and Gardasil 9). HPV vaccines offer the best protection to girls and boys who have time to develop an immune response before being sexually active with another person. That's why HPV vaccination is recommended for preteen girls and boys ages 11 or 12.
"In order for this vaccination to work, administration has to be given prior to the onset of sexual activity," Dr. Hall said. "Most providers would recommend giving this three-course vaccine between the ages of 14 and 24. This effectively prevents the transmission of HPV and significantly limits the likelihood of developing cervical cancer."
To understand the HPV vaccine's effectiveness with different dosages, Dr. Kreimer and team looked at data from two large trials of the vaccine — the Costa Rica Vaccine Trial and the PATRICIA trial.
The Costa Rica trial involved 7,466 Costa Rican women between the ages of 18 and 25. The PATRICIA trial involved 18,644 women globally between the ages of 15 and 25.
Both trials examined the HPV-16/18 vaccine, which aims to protect against HPV types 16 and 18. These two strains cause the most cases of cervical cancer worldwide, according to Dr. Kreimer and team.
All study patients were assigned the usual three doses of the vaccine within six months. Dr. Kreimer and team focused on those women who — for a variety of reasons, including pregnancy — did not receive all three doses.
In total from the two trials, 22,327 women received three doses of the vaccine, while 1,185 women received two doses and 543 received only one dose. These women were then checked for an HPV infection after four years.
At that time, trial researchers found no HPV infections in 77 percent of the women who received all three doses. The same was true for 76 percent of the women who received two doses, and nearly 86 percent of the women who received only one dose.
According to Dr. Kreimer and team, if only one dose of the HPV vaccine is indeed proven effective, these results may greatly improve access to the vaccine worldwide.
"The current recommendation is for three doses over a six-month period," Dr. Hall said. "However, even if three doses are not completed, it is known that partial protection is obtained by obtaining as few as one. I would strongly recommend this regimen for all young teenagers, both boys and girls."
Patients should discuss the best vaccine regimen with their doctors.
This study was published June 10 in the journal The Lancet Oncology.
The NCI, the Ministry of Health of Costa Rica and GlaxoSmithKline (the company that produces the HPV vaccine Cervarix) funded this research.
Several study authors disclosed potential conflicts of interest, such as being employed by or owning shares of GlaxoSmithKline or having ties to Merck (the company that produces Gardasil).