With 23 percent of all reported cancers in women, carcinoma of the cervix is the most common in South Africa . The incidence rate is approximately 35/100 000 women years which represents one of the highest incidence rates in the world.
In the last two decades, the etiological role of the Human Papilloma Virus (HPV) infection in the development of pre-invasive and invasive lesions of the cervix, vagina and the ano-genital region has been conclusively established. The understanding of the oncogenesis of cervical cancer has improved to such an extent that new technologies to detect persistent HPV infection are becoming part of clinical practice.
HPV16 is associated with more than 50% of all invasive carcinomas, HPV18 with 16% and HPV31 with 8%. Protection against the most potent carcinogen is a classic example of primary prevention. HPV 6 and 11 cause genital warts.
Vaccination against infection with specific high risk HPV is now commercially available and is likely to change the future of the disease. It may actually be the only cost-effective long-term strategy in the fight against cervical cancer in South Africa where a high coverage of cervical screening programmes may never be achievable.
An effective HPV16 vaccine would prevent about half of all cervical cancer cases worldwide if the population coverage is adequate. However, a multivalent vaccine that would include HPV18, too, could possibly prevent about two-thirds of such cancers.
Virus-like particles (VLP) are used in the manufacturing of currently available prophylactic vaccines. These vaccines contain no viral DNA capable of replication and are, therefore, non-infectious. They may induce antibody titres much higher than natural occurring infections.
Pharmaceutical companies Sanofi Pasteur and Merck completed extensive testing of a commercial quadrivalent, prophylactic vaccine, which is called Gardasil ® . This vaccine protects against HPV types 16 and 18 (oncogenic) and 6 and 11, which are the two most important types causing genital warts. This vaccine is available in most countries worldwide, including the private sector in South Africa . Another vaccine is GlaxoSmithKline's Cervarix TM , which targets HPV16 and 18. Current data prove protection for the first five years after vaccination. Longer follow-up studies are keenly awaited.
Safety of the vaccine
The vaccine is evidently both safe and effective. (Although there have been some reports on evident adverse events, including three deaths after the administration of Gardasil vaccine, the latest findings put the issue into perspective and explain that the deaths were in all probability not due to the vaccine.) The efficacy and safety of HPV vaccination in the immunocompromised population, for instance pregnant women, HIV-infected women and users of medicines such as steroids, has not been established. Furthermore, with attempts to vaccinate against common HPV types, it is unknown if other new HPV types would dominate or emerge. Moreover, the impact of the vaccine on the future epidemiology of cervical cancer is not predictable.
Internationally, the vaccine is not marketed as a low-cost item. In a health economics equation, the cost of immunisation must be weighed against the cost of screening and treatment for cervical cancer with the understanding that the cost-saving benefits of immunisation will only become apparent in one or two decades and that ongoing screening will be needed for many decades.
Immunogenicity of the vaccine
Bridging studies of immunogenicity conducted among boys and girls aged between 9 and 15 years show that the vaccine is immunogenic across a wide age range, but the greatest immune responses were observed in prepubertal children. The vaccine was immunogenic in 100% of participants across the age range of 10 to 55 years, but antibody response decreases with increasing age.
Schedule for vaccination
It is advisable that vaccination should be administered before sexual debut, the optimal age being 9 or 10. Six months are needed to complete the three doses in the currently available HPV immunisation schedule. It has been demonstrated that the last dose can be given safely within the twelve months of onset of vaccination. If there is a further assumption that a vaccinated individual may require a booster after 10 or so years, it is probably more cost effective to immunise 12 year-olds than infants. Current data prove adequate immunity for 5 years after vaccination.
HPV vaccination in women with existing cytological anomalies has no known benefits.
Males can also be immunized to reduce infection in the population still further even though it is not yet licensed for them. However, the cost of such an intervention may be prohibitive, no important HPV related disease has been shown to be prevented and this strategy will, therefore, not be cost effective.
Ongoing cervical screening
Ongoing cervical screening of the HPV vaccinated women is recommended and required as protection by either vaccine is approximately 75% and not 100%. It may be cost effective to have longer intervals than currently used and it is uncertain whether cytological screening will be the best approach. HPV DNA testing remains a very valuable test to prove infections with high risk HPV types also after vaccination. The available test can show infection not only with HPV16 and 18 but also with other high and medium risk types which may not be covered by the vaccine. Primary screening with HPV testing may be the most appropriate screening policy, with cytological testing of individuals with persistent infections.
The challenge in South Africa is to determine how best to bring this medical breakthrough to the greatest number of people. An essential step is to educate the public, policymakers, legislators and health care providers in order to promote informed decision making. Making HPV vaccination compulsory would have the advantage of creating high levels of immunity, which could indirectly protect other members of the community who have not received vaccines. While some might raise concerns about governmental intrusion on individual decision making, others could oppose the permissible scope of exemptions imposed by parents on their children for religious or philosophical reasons. However, when Section 129 of the new Children's Act (No 38 of 2005) comes into effect, children over the age of 12 will be able to consent to medical treatment.
Document compiled by the South African HPV Advisory Board
An expert panel on human papilloma virus infection and its clinical implications June 2008