How effective is general childhood vaccination against HPV 16 and 18 aimed at preventing cervical cancer?
The issue
Human papilloma virus (HPV) infections are the most common sexually transmitted disease for both women and men. Infection of the cervix by one or more HPVs is a prerequisite for cervical cancer. These infections usually regress spontaneously. However they can persist and develop into cellular changes. In some women these cellular changes progress to cancer. Over 100 HPV types have been identified, 18 of which are high-risk or potentially high-risk types for cervical cancer.
The incidence and mortality of cervical cancer are highest in developing countries and lowest in Western Europe, North America, and Japan. Introduction of organized cervical cancer screening programmes is one reason behind the reduced incidence. These programmes enable early detection and treatment of cellular changes before they become a risk for developing into cancer.
Vaccination against viral infections is a relatively new principle for cancer prevention. Vaccines against HPV are aimed at preventing cervical cancer. Current vaccines target HPV types 16 and 18 and not all cervical cancer-associated HPV types.
Findings
There is strong scientific evidence that vaccination in young women aged 15 to 26 years (showing no signs of past and current HPV 16 or 18 infections at the study onset) provides over 90% protection against severe cellular changes with HPV 16 or 18 (High-grade cervical intraepithelial neoplasias (CIN 2+) positive for HPV 16 or 18). These study results currently offer the closest estimate of the expected preventive effect of vaccinating children.
In children aged 9 to 15 years studies have only evaluated the immune response after vaccination. There is moderately strong scientific evidence that children initially developed an immune response that was equal or superior to that achieved in young women after vaccination.
The effect of general childhood vaccination against HPV 16 and 18 on future morbidity and mortality from cervical cancer is not yet known. One estimate shows that nearly half of the cervical cancer cases would not be prevented by general childhood vaccination against HPV 16 and 18. Therefore organized cervical cancer screening programmes would need to continue.
The current estimated effect of general childhood vaccination against HPV 16 and 18 on the willingness of vaccinated women to participate in organized screening programmes would need to be determined.
Scientific evidence on the cost-effectiveness of general childhood vaccination against HPV 16 and 18, in combination with organized cervical cancer screening programmes is uncertain, and therefore found to be insufficient.
Policy considerations
The effect of general childhood vaccination against HPV 16 and 18 on future morbidity and mortality from cervical cancer is not yet known. Whether or not vaccine against HPV 16 and 18 should be included in a general vaccination programme is a policy issue that concerns, among other things, the level of uncertainty that the public can accept regarding positive and negative effects when allocating resources. Introducing such a programme would require organized, systematic follow up of the outcomes and cost-effectiveness of all preventive interventions against cervical cancer.
Type of evidence
In this systematic review the effectiveness of vaccination in women was based on four randomized controlled trials. The evaluations of the immune response in children were based on one randomized controlled trial and two studies with no control groups. The evidence of cost-effectiveness was based on six model studies from Denmark, Norway, and the USA.
