Human papillomavirus (HPV) is affecting both males and females. Nearly 80%of people will be infected with at least one type of genital HPV at some time. However, HPV causes cervical cancer in women and it’s the fourth most common cancer in women,
Human papillomaviruses (HPV)
Human papillomaviruses (HPV) are a large group of double-stranded DNA viruses which contain more than 100 virus types. They infect squamous epithelial cells of the skin and the mucosal membrane of the anogenital tract through sexual contact.
HPV can be divided into 2 groups: low-risk viruses and high-risk viruses. Low-risk HPVs (such as HPV 6 and 11) cause genital warts which is the most common sexually transmitted disease. There are 15 high-risk HPVs that can cause intraepithelial lesions (which are pre-cancerous), cervical cancer and other cancers affecting the anus, oropharynx, vulva, and vagina, and penis. Of the high-risk HPVs, types 16 and 18 are responsible for about 70% of all cervical cancers.
Three types of vaccines are currently available for the prevention of HPV related disease. All three vaccines are directed against the common high-risk HPV types 16 and 18. These vaccines are prepared from a purified L1 structural protein of the virus and do not contain live biological products or DNA, hence non-infectious.
The bivalent vaccine (Cervarix® ). First licensed in 2007, the bivalent vaccine is directed against HPV types 16 and 18. The quadrivalent vaccine (Gardasil® ). This was first licensed in 2006. It protects against HPV types 6, 11, 16 and 18. It is produced using yeast substrate and also includes amorphous aluminium hydroxyphosphate sulfate.
The nonavalent vaccine (Gardasil®9). This was first licensed in 2014 and is effective against nine HPV types. It contains purified viral L1 protein for HPV 6, 11, 16, 18, 31, 33, 45, 52 and 58.
The bivalent vaccine is indicated for protection against cancerous and pre-cancerous lesions of the anogenital tract while both quadrivalent and nonavalent vaccines also provide protection from common low-risk HPV types (6 and 11) which cause anogenital warts. In fact, the introduction of the quadrivalent vaccine resulted in a rapid reduction in the prevalence of genital warts.
The serological response following vaccination is much stronger than that following natural infection of HPV. This might be related to better activation of lymph node cells by the intramuscular administration of vaccine rather than the mucosal infection. The use of adjuvants in the vaccine may also be a contributing factor.
According to the currently available evidence all three HPV vaccines have relatively similar effectiveness in the prevention of cervical cancer.
Evidence from clinical trials shows that the bivalent and quadrivalent vaccines also provide some cross-protection against high-risk HPV types other than types 16 and 18 (particularly for types 31,33 and 45) which are not originally targeted by them. It is not known whether the nonvalent vaccine provides any cross-protection against HPV types not included in the vaccine.
HPV vaccines are intended to be administered before the onset of sexual activity, therefore, the vaccination schedule depends on the age of the recipient. The vaccines were originally marketed using a 3 dose schedule but a 2 dose schedule was approved later, based on immunogenicity data.
However, a 3 dose series is still recommended for people with immunocompromised conditions such as HIV infection, organ transplantation, autoimmune disease, malignancies and other conditions with impaired cell-mediated/humoral immunity.
Based on currently available data from many large-high-quality studies HPV vaccines are considered to be extremely safe. The adverse events following vaccination include local reactions such as pain, redness and swelling and systemic reactions such as syncope and anaphylaxis. Although a serious adverse event, the risk of anaphylaxis is as low as 1.7 cases per million doses of the vaccine.
Should we vaccinate boys too?
Following the introduction of the HPV vaccine, most countries initiated immunization programs exclusively for women since gender-neutral vaccination is considered less cost-effective than vaccination of girls only.
United States, Canada, Australia and some other countries recommend HPV vaccination for boys and young men as well.
The World Health Organization recommends vaccination of males only if it is feasible, affordable, cost-effective, and does not divert resources from vaccination of the primary target population (girls aged 9-14 years) or from effective cervical cancer screening programs.
However, we should not forget that this infection carries a significant disease burden among males as well as females.
While this infection is the main cause of cervical cancer, it is also a major etiological factor in cancers of the oropharynx, penis, and anus. The incidence of anal cancer among men aged 20-49 is on the rise. The rates are particularly high in men who have sex with men. The number of oropharyngeal cancers related to HPV infection also seems to be increasing over the past 20- 30 years due to the changing sexual behaviours such as the increasing practice of oral sex. Most of these related non-cervical cancers arise in men and there are no effective screening programs for these cancers. In addition, oropharyngeal cancers are difficult to treat and have poor long-term survival rates.
Since the burden of HPV related cancers in men is coming close to that in women, it is imperative that most countries reconsider expanding HPV vaccination to include boys and young men.
Dr. Narmada Ranaweera is a medical graduate from Faculty of Medical Sciences, University of Kelaniya, Sri Lanka. Her academic interests are in anesthesiology and Surgery. She is currently working at Provincial General Hospital Kurunegala as an anesthesiologist at surgical ICU