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HPVワクチン導入で10代の感染率が低下
 2006年のワクチン導入により、子宮頚癌の主要な原因であり性感染症であるヒトパピローマウイルスの危険なタイプの十代の女子の有病率が約半分まで低下している。
 感染率の急激な低下の一方で、使用制限への危惧が出現している。いくつかの徴候がみられ、その一つはワクチンが性感染症を防ぐことから、子どもの性活動の促進への親の心配であり、親が予防接種を受けさせたくないとする割合が増加している。もう一つは、ミネソタ州の共和党のミシェルバックマンのいう「危険な副作用」であるが、保健当局は事実無根としている。
 米国では比較的低いワクチン接種率にもかかわらず、14〜19才の女子のガンを引きおこすウイルス株の感染率は、2006年の7.2%から2010年には3.6%に低下した。
 米国では毎年子宮頚癌にを約12,000人が発症し4,000人が死亡している。CDCの推計によれば、現在のワクチン接種率で、13才以下の女子の45,000人の発症と14,000人の死亡を防げるという。接種率を80%に上げれば、さらに53,000人の発症と17,000人の死亡を防げるという。
 米国人の約7,900万人、多くは十代後半と二十代前半でHPVに感染しており、人口の約1/4にあたる。毎年約1,400万人が感染し、毎年約19,000人の女性のガンを引きおこし、8,000人の男性のガンを引きおこしている。女性では子宮頚癌、男性では咽頭癌が最も多い。
 2種類のワクチンがあり、メルク社のものは男子と女子用、グラクソ社のは女子用である。専門家は、2007年に全ての女子に推奨し、2011年には男子にも拡大した。

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HPV Vaccine Is Credited in Fall of Teenagers’ Infection Rate
http://www.nytimes.com/2013/06/20/health/study-finds-sharp-drop-in-hpv-infections-in-girls.html

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 recent years, a striking measure of success for a vaccine against the virus that was introduced only in 2006, federal health officials said on Wednesday.
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Joe Raedle/Getty Images
Dr. Judith L. Schaechter gives an HPV vaccination to a 13-year-old girl in her office at the University of Miami Leonard M. Miller School of Medicine.
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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 HPV vaccine in the United States. Health departments across the country are scrambling for ways to increase vaccination rates, while nonprofit groups are using postcard reminders and social media campaigns and pediatricians are being encouraged to convince families of the vaccine’s benefits.

There are some signs that resistance to the vaccine may be growing. A study published in the journal Pediatrics in March found that 44 percent of parents in 2010 said they did not intend to vaccinate their daughters, up from 40 percent in 2008. Because it prevents a sexually transmitted infection, the vaccine comes with a stigma. Some parents worry it promotes promiscuity. And it has been controversial. During the Republican primary in 2011, Representative Michele Bachmann, Republican of Minnesota, said the vaccine could have “dangerous side effects,” a concern that health officials say is unfounded.

The magnitude of the decline in HPV infections surprised public health experts because only about a third of teenage girls in the United States have been vaccinated with the full course of three doses. By comparison, vaccination rates in countries like Denmark and Britain are above 80 percent. Even Rwanda, in East Africa, has reached 80 percent.

Yet even with relatively low vaccination rates in the United States, 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, the officials said.

“These are striking results,” said Dr. 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 findings, published online Wednesday in The Journal of Infectious Diseases, covered the years 2003 to 2010 and were based on a national survey that is conducted every two years and is considered the gold standard on health indicators. Government health workers interviewed more than 8,000 girls and women ages 14 to 59 and collected vaginal swabs that were evaluated by the C.D.C.

The infection rate for girls fell even further when the two strains of the virus that cause genital warts were included, with a 56 percent drop over the period of the study. The rate was flat in the years before the vaccine was introduced, giving researchers even more assurance that the vaccine was driving the decline. Health officials began monitoring HPV prevalence in boys only this year. The first data will be available in 2015.

There are about 12,000 cases of cervical cancer and 4,000 deaths a year in the United States. At current vaccination rates, the vaccine would prevent 45,000 cases of cervical cancer and 14,000 deaths among girls now age 13 and younger over the course of their lifetimes, according to C.D.C. estimates. Increasing the rate to 80 percent could prevent an additional 53,000 cancers and nearly 17,000 deaths.

Federal officials on Wednesday sought to dispel fears about the vaccine, and emphasized its role in preventing cervical cancer.

“This is an anticancer vaccine,” Dr. Frieden said.

About 79 million Americans, most in their late teens and early 20s, are infected with HPV, or about a quarter of the American population. 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.

Health officials offered several possible explanations for why the drop was so sharp even though most girls in the United States are still not fully vaccinated.

One possible reason is a phenomenon known as herd immunity, in which people who are vaccinated reduce the overall prevalence of the virus in society, decreasing the chances that unvaccinated people would be exposed to someone who is infected. Another is the unexpected effectiveness of a partial dosage of the HPV vaccine, said Dr. Lauri E. Markowitz, a medical epidemiologist at the C.D.C. and the lead author of the study. About half of teenage girls in the United States have received at least one dose of the vaccine.

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Reduction in Human Papillomavirus (HPV) Prevalence Among Young Women Following HPV Vaccine Introduction in the United States, National Health and Nutrition Examination Surveys, 2003-2010
Lauri E. Markowitz1, Susan Hariri1, Carol Lin1, Eileen F. Dunne1, Martin Steinau2, Geraldine McQuillan3 and Elizabeth R. Unger2
+ Author Affiliations

1Division of STD Prevention, National Center for HIV, Viral Hepatitis, STD, and TB Prevention
2Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention (CDC), Atlanta, Georgia
3National Center for Health Statistics, CDC, Hyattsville, Maryland
Correspondence: Lauri E. Markowitz, MD, Centers for Disease Control and Prevention, 1600 Clifton Rd, MS E-02, Atlanta, GA 30333 (lem2@cdc.gov).
Abstract

Background.?Human papillomavirus (HPV) vaccination was introduced into the routine immunization schedule in the United States in late 2006 for females aged 11 or 12 years, with catch-up vaccination recommended for those aged 13?26 years. In 2010, 3-dose vaccine coverage was only 32% among 13?17 year-olds. Reduction in the prevalence of HPV types targeted by the quadrivalent vaccine (HPV-6, -11, -16, and -18) will be one of the first measures of vaccine impact.

Methods.?We analyzed HPV prevalence data from the vaccine era (2007?2010) and the prevaccine era (2003?2006) that were collected during National Health and Nutrition Examination Surveys. HPV prevalence was determined by the Linear Array HPV Assay in cervicovaginal swab samples from females aged 14?59 years; 4150 provided samples in 2003?2006, and 4253 provided samples in 2007?2010.

Results.?Among females aged 14?19 years, the vaccine-type HPV prevalence (HPV-6, -11, -16, or -18) decreased from 11.5% (95% confidence interval [CI], 9.2?14.4) in 2003?2006 to 5.1% (95% CI, 3.8?6.6) in 2007?2010, a decline of 56% (95% CI, 38?69). Among other age groups, the prevalence did not differ significantly between the 2 time periods (P > .05). The vaccine effectiveness of at least 1 dose was 82% (95% CI, 53?93).

Conclusions.?Within 4 years of vaccine introduction, the vaccine-type HPV prevalence decreased among females aged 14?19 years despite low vaccine uptake. The estimated vaccine effectiveness was high.

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