The human papillomavirus (HPV) is formed by circular DNA molecules of 8,000 base pairs in length and enveloped by a protein shell composed of 2 molecules. There are more than 120 types described, of which only 15 are considered high risk for the development of cervical cancer.
The cycle begins when infectious particles reach the basal layer of the epithelium through small tears. There they join the cells and penetrate them. It has been suggested that, to maintain the infection, the virus must infect an epithelial stem cell.
HPV infection is asymptomatic and most cases resolve spontaneously: 70% during the first year and 90% in the first 2 years, offering subsequent protection against reinfections. The remaining percentage evolves into epithelial neoplastic changes that lead to low-grade precancerous lesions that also spontaneously remit in 60% of cases. The rest of the cases progress to high-grade precancerous lesions that can lead, if left untreated, to a cervical cancer whose evolution requires between 30 and 40 years.
HPV is transmitted almost exclusively through sex. Its prevalence among the female population stands at 10-15% from 30-35 years worldwide, although with important territorial differences. In Spain, the average rate, in the low segment, is around 3%. At younger ages, the rates are higher, but most of these viral presences disappear spontaneously, without sequelae, throughout the first or second year.
The tetravalent vaccine is indicated in the prevention of high-grade cervical dysplasia (CIN 2/3), cervical carcinoma, high-grade vulvar dysplastic lesions (VIN 2/3) and external genital warts (condyloma acuminata) causally related to types 6, 11, 16 and 18 HPV.
The ultimate long-term goal of the HPV vaccine is the prevention of invasive cervical cancer. Other associated objectives are the prevention of other HPV-related cancers: vulva, vagina, anus and penis and, probably, oropharynx. In the short and medium term it is intended to prevent precursor lesions of cervical cancer, intraepithelial neoplasm of the cervix and CIN, especially the considered necessary precursor lesion, CIN 3. In addition, the tetravalent vaccine raises the short-term possibility of preventing genital warts / condylomas and recurrent respiratory papillomatosis, caused by HPV types 6 and 11.
The tetravalent vaccine includes virus-like particles (VLP) of types 6, 11, 16 and 18, and uses an aluminum salt as an adjuvant. The recommended vaccination schedule after clinical development is composed of 3 intramuscular doses of 0.5 ml. The second dose is given at 2 months of the first and the third at 6 months. It is not necessary to administer booster doses.