Human papillomavirus (HPV) and why it is important to vaccinate
There are over 100 subtypes of HPV virus. About 40 or so strains are implicated in genital infections. The genital strains are very infectious and can be transmitted by oral, genital, anal and even genital-to-genital non-penetrating contact. It has been estimated than more than 80% of the population will get 1 or more infections with one of these genital strains. According to the CDC, presently almost 80 million Americans are infected with a genital strain of HPV and about 14 million acquire infection yearly. Being infected with 1 strain does little to protect against infection with a different genital strain.
The virus grows very slowly so Infections with these strains are often not clinically apparent or take time to develop symptoms. In women the most common manifestation of infection is an abnormal cervical Pap smear. Fortunately, most women cure these infections over a 1-2 year period of time. However, in a small percentage of women the infection becomes chronic and may even progress to cancer years to decades later. This is especially true if infected with one of the more virulent, cancer-causing strains. In women, HPV is also known to cause vaginal, vulvar, anal, and oropharyngeal cancers. In men, cancers caused by HPV include penile, anal, and oropharyngeal cancers. The list of cancers with an HPV association is growing.
The following is estimation by the CDC of yearly cancers caused by genital strains of HPV:
- Over 10,000 cervical cancers
- 2,100 vulvar cancers
- 500 vaginal cancers
- 600 penile cancers
- 2,800 anal cancers in women and 1,500 anal cancers in men (this number is increasing)
- 1,700 oropharyngeal cancers in women and 6,700 oropharyngeal cancers in men (this number is increasing)
This means over 17,000 cancers a year in women and almost 9,000 cancers a year in men are attributed to infection from HPV genital strains. In addition, as noted above, the anal and oropharyngeal cancer toll from HPV is increasing.
In addition to abnormal Pap smears and cancer, about 360,000 persons get genital warts from HPV annually. That translates to 1,000 cases a day. The good news is that the wart-causing strains rarely cause cancer. Many infected, highly-contagious individuals do not have any visible lesions while some develop ugly genital region warts. More bad news, a pregnant mother harboring one of the wart-causing strains may infect her newborn causing Recurrent Respiratory Papillomatosis (RRP), a dreadful malady of warts infecting the vocal cord area. These children develop progressive breathing problems requiring several years of repeated trips to the operating room for treatment.
The epidemiology of infection with genital strains of HPV for men is different than in women. Women typically develop the infection in late teen and early adult years and the incidence of infection slowly lessens after age 30 or so. Men typically acquire HPV infection in their 20’s and 30’s and the drop in frequency of infection and the disappearance of HPV infection occurs far more slowly.
Although there is no specific HPV anti-viral medication, the lesions are amenable to a variety of treatments if discovered early enough. Screening tests in women (and in some high risk men) are available. Preventive measures include education, appropriate use of condoms, newborn circumcision (a decision made by parent and health care provider), and vaccination.
Two vaccines are available in the US. Both provide protection against HPV strains 16 and 18. These 2 strains account for about 70% of the HPV cancers in the US. One of the vaccines also protects against HPV strains 6 and 11- the cause of almost all genital warts. To be protective, the vaccines must be given prior to exposure with that HPV strain. That is one of the reasons the vaccines should be given prior to any sexual contact.
In addition, vaccinating young teens has also been shown to give a more robust immunologic response than waiting until they are older. Over 100 million doses have been given worldwide so far without a safety signal, making it one of the safest vaccines available. Several studies published so far have shown the antibody response to persist. The vaccine is already reaping benefits with studies showing a significant reduction in HPV disease and cervical dysplasia. The real anticipated payoff will occur in the next decades when cancers caused by this virus will hopefully become as unusual as smallpox, polio, and all of the other illnesses we now protect with vaccines.