There are over 200 strains of HPV. Of those, several have gained attention, as they are considered virulent and related to cervical cancer or genital warts. The high risk strains are 16, 18, 31, 33, 39, 45, 51, 52, 56, 58, 59, and 66, and have been related to the development of cervical cancer. Two low risk strains, 6 and 11, are related to genital warts that are typically noncancerous. While the most commonly received vaccine for HPV is the quadrivalent vaccine Gardisil-4, which vaccinates against four types (16, 18, 6, 11) of HPV, the remainder of high risk strains have yet to be covered. Aside from the four strains covered by Gardisil-4, vaccines should also be made to cover HPV 51 and 53. This suggestion is based on a study done on women with squamous intraepithelial lesions. The study revealed that after the top two most common strains of HPV found, 16 and 31, the next most common strains were 51 and 53, which accounted for 21% of HPV cases. Other strains, such as 31 and 45, do not need their own vaccine since both are closely related to strains 16 and 18 respectively. Thus, the Gardisil-4 vaccine provides cross-protection for those strains though they are not directly targeted.
The best time to administer the vaccines would be early childhood. Studies have shown that development of antibodies against HPV is inversely related to age. One explanation could be that pre-adolescents are still building their immune systems and are more likely to have a stronger reaction to the vaccine. Another explanation is that many older women have already been exposed to HPV, rendering the vaccination ineffective. Since the vaccine is a prophylactic, it is unlikely to benefit those who were already infected by HPV.
Due to high development costs, not all strains of HPV can be covered by vaccination. Including research and manufacturing costs, it costs approximately $200-500 million to develop a new vaccine. Another financial barrier is cost of administration, especially in developing countries. Many facilities are not equipped with pre-adolescent health care services. If new HPV vaccines were developed, it is ideal to focus on the most prevalent, cancer-causing strains. Cervical cancer is responsible for nearly 91% of HPV-related cancer deaths. Protection against more strains would produce a global net benefit that heavily outweighs financial costs. The most benefit would be achieved with high coverage of females, since females directly benefit from the vaccination. Males could also receive the vaccine and add an indirect protection for females, though the net benefit of male vaccination is less than female vaccination.
The topic of HPV vaccinations makes me think about my other class on global health. HPV is a widespread disease that is of high global priority. It is unfortunate that the places most direly need protection do not have the resources to benefit from or even receive that protection.
Cutts, F. T., Franceschi, S., Goldie, S., Castellsague, X., de Sanjose, S., Garnett, G., Edmunds, W. D., Claeys, P., Goldenthal K. L., Harper, D. M., Markowitz, L. (2007). Human pappilomavirus and HPV vaccines: a review. Bulletin of the World Health Organization, 85(9), 649-732.
GM Clifford, RK Rana, S Franceschi, JS Smith, G Gough, JM Pimenta. Human papillomavirus genotype distribution in low-grade cervical lesions: comparison by geographic region and with cervical cancer. Cancer Epidemiol Biomarkers Prev2005; 14: 1157-64.
Smith JF, Brownlow MK, Brown MJ, Esser MT, Ruiz W, Brown DR. Gardasil antibodies cross-neutralize pseudovirion infection of vaccine-related HPV types.23rd International Papillomavirus Conference and Clinical Workshop Abstract PL 1-6, Prague, September 1-7 2006.