NEW YORK — 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.
This is a striking measure of success for a vaccine against the virus that was introduced only in 2006, federal health officials said on Wednesday.
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 US.
Health departments across the country are scrambling for ways to increase vaccination rates, while 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 per cent of parents in 2010 said they did not intend to vaccinate their daughters, up from 40 per cent in 2008. Some parents worry the vaccine promotes promiscuity.
Also, 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 US have been vaccinated with the full course of three doses. Yet, infection with the viral strains that cause cancer dropped to 3.6 per cent among girls aged 14 to 19 in 2010, from 7.2 per cent 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 on 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. Government health workers interviewed more than 8,000 girls and women aged 14 to 59 and collected vaginal swabs.
Federal officials on Wednesday sought to dispel fears about the vaccine and emphasised its role in preventing cervical cancer.
“This is an anti-cancer vaccine,” said Dr Frieden.
There are currently two HPV vaccines, one made by Merck for boys and girls, and one by GlaxoSmithKline, for girls.
Health officials offered several possible explanations for why the drop was so sharp even though most girls in the US 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 CDC and the lead author of the study.
About half of teenage girls in the US have received at least one dose of the vaccine.
Because girls and women who got vaccinated tended to be more sexually active, compared with those who were not vaccinated, researchers suggest that those who had been contributing most to the prevalence of the infection were no longer infecting others.
In Singapore, two vaccines — Gardasil and Cervarix — are currently approved for use. Cervical cancer is one of the top 10 cancers affecting women in the country, according to the National Cancer Centre Singapore. AGENCIES
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