"This information will help inform future cervical cancer screening guidelines and continue to decrease deaths from this preventable disease", added Schmeler, who was not involved in the study. Infection with HPV types targeted by the vaccine has declined by almost two-thirds among teenage girls since HPV vaccination was recommended in the United States, according to a study that also found that there was a decrease in HPV infections among women 20 to 24.
So the HPV test comes back positive for many younger women who are newly infected but who will probably clear it without it causing the damage that leads to cancer.
The randomized, controlled study - the kind of trial considered the "gold standard" of research - showed that the human papillomavirus test is more sensitive than the Pap smear, a widely used test that has been a standard part of women's preventive health care for decades but has drawbacks.
"What our study shows is that by using HPV testing, we detect precancerous lesions earlier", says lead author Dr. Gina Ogilvie.
"In our world this study is going to be a pretty big deal, in a good way", says Dr. Kathleen Schmeler, a gynecologic oncologist at the University of Texas MD Anderson Cancer Center.
Though the researchers also determined that adding cytology testing after a positive HPV screen detected very few new events, it wasn't totally fool-proof: by virtue of the trial design, women who were found to be HPV-negative also received cytology screening at 48 months - and an additional three grade 2 lesions were found among those participants. At the end of four years, both groups received both tests.
None of the methods yielded fully accurate results.
Smear tests look for changes to cells of the cervix, while HPV testing looks for the presence of the virus. But the newer, more accurate HPV test may replace the Pap smear as the preferred screening test, Ogilvie said. He said that physicians will have to make the choice between HPV testing and co-testing based on cost-effectiveness studies and their own discretion, while continuing to improve outreach for underserved and inadequately screened women to combat such high rates of cervical cancer. They also found that women with negative HPV test were more likely to not have cancer for the next four years, compared to the ones that had a negative Pap test.
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Women who tested negative for HPV were recalled after 48 months for both HPV and smear tests, while those who had a negative smear test were recalled after 24 months for a repeat smear test, then again at 48 months for both tests.
The human papillomavirus (HPV) causes 99 percent of all cases of cervical cancer, according to the National Cancer Institute.
"In the US, co-testing is now the recommended gold standard, and neither doctors nor their patients should be willing to give up the added benefit you get from screening with a Pap test and HPV test together", he says.
Several experts predicted the results would spur efforts to entirely replace the Pap test with the HPV test. About 4,200 women will die of the disease.
The study included patients from 2008 to 2012, and nearly half of them were tested using the HPV test. However, if the virus persists until their 30s, that's when it becomes a problem. He wrote in an email that this new study actually shows the small but significant benefit of co-testing.
One limitation of the study was that it was done in a specific area of Canada and the findings may not be generalized to other populations. Women also filled out questionnaires about lifestyle and sexual health history to ensure differences in results were not down to imbalances between the test groups.
"At the moment, at most, we may be vaccinating at most 30 to 40 percent of girls".