The vaccine for the Human Papillomavirus (HPV) is proving to have significant population-level effects in Connecticut, with rates of precancerous lesions caused by HPV down drastically among young women, a new Yale School of Public Health study finds.
The study used data collected between 2008 and 2015 and revealed that rates of cervical lesions caused by HPV, known as cervical intraepithelial neoplasia grades 2-3 and adenocarcinoma in situ (CIN2+), declined in that period by between 30 percent and 74 percent among women 21 to 26 years old. The total number of cases reported declined over this period from 2,163 in 2008 to 1,540 in 2015.
Led by Associate Professor Linda Niccolai, Ph.D., the study makes use of a data set from the Connecticut Department of Public Health, which began requiring mandatory reporting of CIN2+, an important indicator of risk of future cervical cancer, in 2008. Cervical lesions have important health consequences, high associated costs and cause significant psychological stress to those who are diagnosed with them.
"Monitoring impact of HPV vaccines is critical for assessing the progress of our immunization programs and for ensuring the population is benefitting," said Niccolai. "We are in a unique position in Connecticut to do this for precancerous cervical lesions, a clinically relevant outcome. The impacts that we are seeing are very exciting, and at the same time, indicate that more work needs to be done to drive the rates even lower."
According to the Centers for Disease Control and Prevention (CDC), HPV is the most common sexually transmitted infection in the United States, with about 79 million Americans currently infected. While many HPV infections go away on their own, some can develop into cervical and other types of cancer. The HPV vaccine was introduced in 2006, and is recommended for both boys and girls at ages 11 and 12 years.
The data used in the study was collected through the Emerging Infections Program (EIP), a collaboration between the CDC, the Connecticut Department of Public Health and the Yale School of Public Health. EIP conducts surveillance and analysis of emerging infections in the state. The data are used to measure the success of vaccination programs as well as monitoring other infectious diseases and the results often contribute to policy decision-making.
The team was able to determine that the HPV vaccine was most likely behind the declining cervical lesion rates, rather than other potential factors such as changes in screening rates or related risk behaviors. One challenge cited by the team in analyzing trends such as this is the difficulty in disentangling one cause behind a trend from others. To address this, the team used advanced statistical approaches as well as additional data sets to compare findings to changes in HPV vaccination coverage; rates of Pap screening, a necessary screening test for the diagnosis of CIN2+; and changes in the sexual behaviors that place people at risk for HPV.