By Ben Werschkul, Alyssa Kim, Marcus Mabry, Pedro Rafael Rosado, Kriston Lewis, Robin Lindsay and Abe Sater
The Success of the HPV Vaccine: The Times's Pam Belluck on how the HPV vaccine has helped drastically reduce the number of human papillomavirus cases among teenage girls.
The prevalence of dangerous strains of the human papillomavirus — the most common sexually transmitted infection in the United States and a principal cause of cervical cancer — has dropped by half among teenage girls in the last decade, a striking measure of success for a vaccine that was introduced only in 2006, federal health officials said on Wednesday.
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Dr. Judith L. Schaechter gives an HPV vaccination to a 13-year-old girl in her office at the the University of Miami Leonard M. Miller School of Medicine.
Infection with the viral strains that cause cancer dropped to 3.6 percent among girls ages 14 to 19 in 2010, from 7.2 percent in 2006, a new study has found. The vaccine protects against strains of the HPV virus that cause 70 percent of cervical cancers.
“These are striking results,” said Thomas R. Frieden, director of the Centers for Disease Control and Prevention. “They should be a wake-up call that we need to increase vaccination rates. The bottom line is this: It is possible to protect the next generation from cancer, and we need to do it.”
The study, published in the June issue of The Journal of Infectious Diseases, covered the years 2003 to 2010. Its findings were based on a national survey that is conducted every two years and considered the gold standard on health indicators. Government health workers did face-to-face interviews and collected vaginal swabs from more than 8,000 girls and women ages 14 to 59 that were sent to the C.D.C. for evaluation.
The decline surprised public health experts because vaccination rates in the United States are still relatively low. Only about a third of teenage girls have been vaccinated with the full course of three doses, far lower than in other rich countries like Denmark and Britain, where vaccination rates are above 80 percent. Even Rwanda, a developing country in central Africa, has reached 80 percent.
Dr. Frieden said the low vaccination rate in the United States means that 50,000 girls alive today will eventually develop fatal cervical cancer, deaths that could have been prevented if the country’s rate had been at 80 percent. For every year the rate lags, another 4,400 girls will develop cervical cancer in their lifetimes, he said.
Health officials offered several possible explanations for why the drop was so sharp despite the fact that most teenage girls in the United States are still not fully vaccinated.
One possible reason is a phenomenon known as herd immunity, in which vaccinated people reduce the overall prevalence of the virus in society, reducing the chances that unvaccinated people would have sex with someone who is infected. Another is the unexpected effectiveness of a partial dosage of the vaccine, Dr. Markowitz said. About half of teenage girls in the United States have gotten at least one dose of the vaccine.
The sharp decline in the infection rate comes at a time of deepening worry among doctors and public health officials about the limited use of the vaccine in the United States and some signs that resistance to it may be growing. A study published in Pediatrics in March found that 44 percent of parents in 2010 said they did not intend to vaccinate, up from 40 percent in 2008.
Many parents fear the vaccine will have bad side effects, a concern that health officials say is unfounded. Others worry that girls will see the vaccines as condoning sex.
Dr. Frieden said that doctors had been one of the main obstacles to increasing vaccination rates. They are “not consistently giving strong recommendations for the vaccines, particularly for younger teens,” he said. Another factor is skeptical parents, who commonly say that the vaccine is not needed because their teenagers are not having sex. But Dr. Frieden said vaccination should happen long before a person is exposed.
“The time has come to ramp up our efforts to protect the next generation against cancer,” he said. “This is an anti-cancer vaccine.”
About 79 million Americans, most in their late teens and early 20s, are infected with HPV. Each year, about 14 million people become infected. The virus causes about 19,000 cancers in women every year, and 8,000 in men, according to the C.D.C. Cervical cancer is the most common among women; among men, throat cancer is most common.
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