MONDAY, Nov. 4 (HealthDay News) -- Just one dose of a human
papillomavirus (HPV) vaccine may be enough to provide long-term
protection against cervical cancer in women, a new study
The HPV vaccine is currently recommended as a three-dose series,
but doctors have found it difficult to finish out the series for
However, the researchers discovered active human papillomavirus
antibodies in Costa Rican women four years after they had received
only one dose of Cervarix, a vaccine that protects against two HPV
The study also found that women who received two doses six
months apart appeared to have just as much antibody protection
against HPV as those who received three doses.
Funded by the U.S. National Cancer Institute (NCI), the study
was published in the November issue of
Cancer Prevention Research.
HPV vaccination rates in the United States are low. In 2012,
only about 54 percent of girls even received one dose, and just 33
percent went on to receive all three shots, according to a recent
report from the U.S. Centers for Disease Control and
But the impact of only having to get one or two doses of the
vaccine would be felt most in developing countries, where cervical
cancer death rates are higher but the high cost of the vaccine
makes it difficult to protect all women.
"Vaccination with two or even one vaccine dose could simplify the logistics and reduce the cost of vaccination in the developing world, where more than 85 percent of cervical cancer occurs and it is the most common cause of cancer death in women," said study author Mahboobeh Safaeian, an investigator in the NCI's division of cancer epidemiology and genetics.
More than 275,000 women die from cervical cancer each year
worldwide, making it the sixth-leading cause of cancer death,
according to the World Health Organization. In the United States,
active screening programs have reduced the cervical cancer death
rate to about 3,900 women a year, according to the CDC.
HPV vaccine doses run about $130 apiece, according to the
American Cancer Society, and cost is a big consideration, one
"If you reduce the cost by a third, you can give it to three times as many people," said Dr. Shashikant Lele, clinical chief of gynecologic oncology at Roswell Park Cancer Institute, in Buffalo, N.Y. "If one dose is adequate to protect, we can vaccinate three times the number of women with the same amount of money."
Researchers made these findings during a clinical trial to test
the effectiveness of Cervarix in women from Costa Rica.
They measured immune response to the vaccine in blood samples
drawn from 78, 192 and 120 women who received one, two and three
doses of the vaccine, respectively.
The doctors then compared those results to data from 113 women
who were not vaccinated but had antibodies against the viruses in
their blood because they had been infected with HPV in the
Up to four years later, all of the women in all three
vaccination groups had antibodies for HPV 16 and 18, the two
strains Cervarix guards against.
Although antibody levels among women who received one dose were
lower than among those who received three doses, the levels
appeared stable, according to the researchers, which suggests that
these are lasting responses.
Moreover, the levels of antibodies in women from the one- and
two-dose groups were between five and 24 times higher than the
levels of antibodies in women who were not vaccinated but were
infected with HPV.
The contents of the HPV vaccine might provide another
explanation, Safaeian said.
The vaccine is created using genetically engineered versions of
the virus that prompt an immune response but do not have the
ability to multiply and cause illness, she explained.
This type of vaccine might cause a stronger immune response than
vaccines made from parts of live viruses (such as the tetanus
vaccine) which often require periodic boosting to maintain
immunity, Safaeian said.
Debbie Saslow, director of breast and gynecologic cancer for the
American Cancer Society, called the findings "very exciting."
"This would be absolutely amazing if we could only give one dose," she said.
However, Saslow noted a few concerns. For one thing, the study
did not involve the HPV vaccine used 99 percent of the time in the
United States -- Gardasil, which guards against four strains of the
virus, she noted.
Also, researchers could only verify protection for four years
after receiving the dose. "If we are vaccinating girls at age 12,
we need to make sure that immunity lasts," Saslow said. "We don't
know, and they don't know, if having three doses will last any
longer than one dose."
Finally, she pointed out that a very small number of women were
involved in the Costa Rican study, and recommended that these
results be verified by tracking girls in the United States who are
receiving the vaccine.
"We need to set up some sort of surveillance system for those who only got one or two doses," Saslow said. "If we're identifying those girls, let's see if we can follow them. We don't need to start a big randomized trial. We can look back using medical records."
Visit the U.S. National Cancer Institute to learn more about
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