by ecancer reporter Clare Sansom

Infection by certain types of the human papilloma virus (HPV) is responsible for almost all the approximately 500,000 cases of cervical cancer diagnosed worldwide each year.

Other less common cancers that can be attributed to variants of HPV include those of the anus, penis, vulva, mouth and throat. 

This virus is transmitted through sexual contact – it is the most common sexually transmitted virus in much of the developed world – and infections are most prevalent in sexually active young people, including adolescents.

Over a hundred different types of HPV have been identified, and over thirty of these are known to be transmitted sexually. 

However, only about fifteen of these (the so-called “high risk” types) have been associated with the transmission of cancer and other serious disease. 

Most cases of cancer arise from infection with either HPV 16 or HPV 18, and infections by these two HPV types cause about 22,000 cases of cancer each year in the US alone, roughly two-thirds being cervical cancer in females.

Vaccination of previously uninfected individuals against specific HPV variants is effective in preventing infection and, therefore, the development of genital warts or more serious disease. 

Two non-infective, bioengineered vaccines are currently available; Gardasil^®, developed by Merck & Co., New Jersey, USA, protects against infection by HPV types 6, 11, 16 and 18, whereas Cervarix^®, developed by GSK, UK, protects against the greatest-risk types 16 and 18 alone. Both vaccines have been approved by the FDA for use in females although only Gardasil is approved in males. 

As the vaccines are only completely effective if given before the recipients become sexually active, and as antibody responses are highest between the ages of nine and 16, they are generally offered in late childhood or early adolescence.

The American Academy of Pediatrics has recommended the vaccination of all 11- and 12-year-old girls since 2007, and it has now updated its guidelines to recommend, rather than simply permit, vaccination of boys at the same age [1].

The new recommendations for the vaccination of both genders have been summarised in the journal Pediatrics [2].

The Academy recommends that all 11- and 12-year-old girls should receive three doses of either vaccine, with the second vaccination 1-2 months and the third one six months after the first.

Boys of the same age should receive three doses of Gardasil at the same spacing. 

All boys and men between 13 and 21 years of age, and girls and women between 13 and 26 years of age who have not already been vaccinated, should also receive the vaccine. 

Neither prior sexual activity nor known HPV infection should be a contra-indication for vaccination, and the availability of vaccination does not change current practice in sexual health counselling.

Furthermore, as the vaccines available only protect against the most common high-risk virus types, vaccinated females are recommended to continue cervical screening.

The Committee on Infectious Diseases, which made the recommendations, cites data from clinical trials and post-registration surveillance as evidence for the efficacy and safety of both vaccines.

Both vaccines are proven to elicit antibody responses that persist for at least several years and to provide protection against diseases caused by the virus types present, including general warts, in sexually active young people.

However, certain conditions including pre-cancerous lesions of the penis in males are too rare for any of the studies carried out so far to have shown protection at a statistically significant level. 

Continued surveillance of over 40 million vaccinations by the Vaccine Adverse Effect Reporting System has identified no severe adverse effects other than very rare allergic responses to vaccine components.

References

[1] Centers for Disease Control and Prevention. Recommendations on the use of quadrivalent human papillomavirus vaccine in males —Advisory Committee on Immunization Practices (ACIP) (2011). MMWR Morb Mortal Wkly Rep. 60(50), 1705-1708

[2] American Academy of Pediatrics Committee on Infectious Diseases (2012). Policy Statement: HPV Vaccine Recommendations. Pediatrics, published online ahead of print February 27, 2012. doi:10.1542/peds.2011-3865