Estimating the number needed to vaccinate to prevent diseases and death related to human papillomavirus infection

Abstract

4 46 64 4 O ver 40 human papillomavirus (HPV) genotypes are known to infect the anogenital tract.1 The International Agency for Research on Cancer has classified these types as being of either high oncogenic risk or low oncogenic risk according to their association with cervical cancer.2 About 70% of all cases of cervical cancer can be attributed to HPV types 16 and 18, 2-4 which are of high oncogenic risk, and about 90% of all cases of genital warts are associated with HPV types 6 and 11, 5,6 which are of low oncogenic risk.Two HPV prophylactic vaccines are currently in clinical trials: one targets HPV types 6, 11, 16 and 18, and the other targets types 16 and 18. Recent large, randomized, placebo-controlled trials have shown that the one targeting types 6, 11, 16 and 18 significantly reduced the incidence of type-specific anogenital and cervical lesions among women not previously infected with these virus strains.7,8 Given its efficacy and safety, this vaccine is now licensed for use in Canada and many other countries. 9,10"Number needed to treat" has been used to describe the population outcome of chronic disease treatments. By analogy, "number needed to vaccinate" has been used for vaccine preventable diseases.11 The number needed to vaccinate can be a helpful measure to illustrate the potential benefit of HPV vaccination, since it combines both the effect of vaccine efficacy and the age-specific background incidence of disease.Because many of the benefits of prophylactic HPV vaccines will occur in the medium to long term, mathematical models are needed to project the impact of vaccination beyond the time horizon of clinical trials. The development of models are based on assumptions, which inevitably cause a level of uncertainty. In the case of HPV vaccination, it is particularly important to quantify the uncertainty surrounding model predictions, because the natural history of HPV is complex (it encompasses numerous stages of disease that depend on HPV type, screening and treatment) and the scientific literature on age-and type-specific natural history and transmission is limited.12 Furthermore, important questions remain regarding HPV prophylactic vaccines, such as the duration of vaccine protection and the overall efficacy of the vaccines against cervical cancer (since surrogate outcomes were used for cervical cancer in clinical trials). 13 We sought to estimate the number needed to vaccinate to prevent HPV-related diseases and death and to quantify uncertainty around model predictions.

Cost-effectiveness of a tetravalent human papillomavirus vaccine in Germany

“…The number needed to vaccinate (NNV) to prevent cases of cervical cancer is a useful measure of vaccine effectiveness (Brisson et al 2007a). Using the natural history model, the NNV with the tetravalent HPV vaccine in Germany was estimated.…”

“…Using the natural history model, the NNV with the tetravalent HPV vaccine in Germany was estimated. NNV was defined as the number of 12-year-old girls that are needed to be vaccinated to prevent an HPVrelated event during their lifetime, calculated as follows: NNV = 1/ARR, with ARR representing attributable risk reduction (Brisson et al 2007a).…”

Childhood Immunization: When Physicians and Parents Disagree

“…Other types of vaccine may raise different considerations, depending on data about risks, benefits, and long-term effectiveness, goals of the vaccination program, and other factors, but they are beyond the scope of this article. [4][5][6][7][8] We consider the ethical, legal, and clinical issues raised by 3 aspects of our scenario: (1) physician counseling; (2) parental decision-making; and (3) deciding whether to continue the physician-patient relationship despite disagreement.…”

Human papillomavirus vaccine for children and adolescents

“…In the Canadian context, modelling has predicted that eight girls would need to be vaccinated to avoid one case of genital warts, 324 to avoid one case of cervical cancer and 729 to avoid one death from cervical cancer (37). The Canadian costs per quality-adjusted life year are between $21,000 and $31,000 (38).…”