Human Papillomavirus, better known as HPV, is a sexually transmitted infection that affects approximately 79 million mostly young Americans. In recent years, health care providers and researchers have led a concerted effort to stop the spread of HPV and for good reason – not only is HPV the most common infection among Americans, HPV infection causes several types of cancers, including cervical cancer, anal cancer, and cancers of the throat, base of the tongue and tonsils. [1] According to the CDC, every year in the United States, HPV causes 33,700 cases of cancer in men and women.[2]
HPV is the root cause of nearly all cases of cervical cancer.
In fact, the CDC estimates HPV infection leads to nearly 11,000 cases of cervical cancer per year. [3] Cervical cancer is cancer of the cervix, a part of the female anatomy situated almost like a tunnel between the upper part of the vagina and lowest portion of the uterus. Cervical cancer develops as a result of gradual yet progressive changes to the normal cells which line the outer surface of the cervix.
Doctors rely on regular Pap smears and other tests to diagnose and classify abnormal cervical cells based upon their microscopic features. Depending on their characteristics, the abnormal cells are classified as low or high risk for progression to cervical cancer. Cervical Intraepithelial Neoplasia (CIN) 2 or 3, more generally known as CIN 2+, are classifications used for abnormal cervical cells associated with a high risk of progression to cervical cancer.[4]
HPV vaccination can significantly reduce the risk of cervical and other forms of cancer which gradually develop in people infected with certain types of HPV.
Fortunately, through school-based initiatives and education of both children and adults, the United States has seen an increase in the numbers of girls, boys, young women and men who undergo HPV vaccination. Between 2013 and 2017, the rate of vaccination in adolescence has increased 5% each year. According to the CDC, 49 percent of adolescents received the full series of HPV vaccine shots. Promisingly, 66 percent of adolescents ages 13-17 years received at least the first dose of the vaccine series.
We wrote in 2014 that the effectiveness of HPV vaccine in preventing cervical and other forms of cancers is proven by data. The data is even more compelling today. On June 26, 2019, a team of researchers on behalf of the HPV Vaccination Impact Study Group published the results of a systematic review and meta-analysis of studies published between February 1,2014 and October 1, 2018. Together, these studies included data related to 60 million girls, boys, women and men in fourteen high-income countries over the course of eight years. The review shed insights on the impact of HPV vaccination in the prevention of HPV infections and related diseases.
The researchers focused on studies which compared the frequency of at least one of three HPV related conditions- genital HPV infections, anogenital wart diagnoses, or histologically confirmed CIN2+.
[1] CDC-Genital HPV Infection – Fact Sheet. https://www.cdc.gov/std/hpv/stdfact-hpv.htm. November 16, 2017.
[2] CDC – How Many Cancers Are Linked with HPV each Year? https://www.cdc.gov/cancer/hpv/statistics/cases.htm. August 15, 2018.
[3] Id.
[4] UpToDate – Cervical intraepithelial neoplasia: Management of low-grade and high-grade lesions. https://www.uptodate.com/contents/cervical-intraepithelial-neoplasia-management-of-low-grade-and-high-grade-lesions. April 30, 2018.
Analysis showed that in the first nine years after the start of HPV vaccination, HPV 16 and 18 infections, anogenital wart infections, and CIN2+ were significantly decreased among the girls and women in the study. More specifically, when the researchers looked at the period from 5 to 8 years post-vaccination, the prevalence of HPV 16 and 18 among girls age 13-19 decreased by 83%. Similarly, infections decreased by 66% among women aged 20-24 years.
By analyzing individual outcomes 5 to 9 years post vaccination, the researchers had a unique opportunity to measure the impact of HPV vaccination on the development of CIN2+, a cervical cancer precursor which itself can take years to develop from the onset of infection with HPV. The analysis showed that 5 to 9 years after vaccination, CIN2+ in girls age 15 to 19 years of age fell by 51%. The rate of CIN2+ fell by 31% among women age 20 to 24.
As the researchers observed, these findings with respect to CIN2+ may impact guidelines for cervical cancer screening, including a shift towards screening women starting at an older age or at longer screening intervals.
The study revealed other important observations related to the increasing rates of vaccination.
One of those observations is what’s known as the “herd effect”. Herd effect applies to diseases spread from person, and occurs when the rate of disease in an unvaccinated group of people is reduced indirectly when vaccination of another group of people reaches a certain level. Here, the researchers found the diagnosis of anogenital warts among boys and men decreased significantly in countries with programs of vaccination limited to girls only. The researchers also observed greater declines in HPV infection related conditions in 1. countries where multiple ages of girls are vaccinated as opposed to countries where only a single age of girls are vaccinated and 2. countries with high routine vaccination coverage > 50% as opposed to low vaccination coverage (<50%).
Americans incur needless health care costs, suffering and death related to preventable HPV related cancers, including cervical and valvular cancer in women and anal and oropharyngeal cancers in both men and women. As this important body of research shows, a concerted effort to encourage increased rates of HPV vaccination could move us closer to the goal of somebody eliminating cervical and other forms of deadly cancers.