Evaluating human papillomavirus vaccination programs in Canada: should provincial healthcare pay for voluntary adult vaccination?

Abstract Background Recently, provincial health programs in Canada and elsewhere have begun rolling out vaccination against human papillomavirus for girls aged 9–13. While vaccination is voluntary, the cost of vaccination is waived, to encourage parents to have their daughters vaccinated. Adult women who are eligible for the vaccine may still receive it, but at a cost of approximately CAN$400. Given the high efficacy and immunogenicity of the vaccine, the possibility of eradicating targeted types of the virus may be feasible, assuming the vaccination programs are undertaken strategically. Methods We develop a mathematical model to describe the epidemiology of vaccination against human papillomavirus, accounting for a widespread childhood vaccination program that may be supplemented by voluntary adult vaccination. A stability analysis is performed to determine the stability of the disease-free equilibrium. The critical vaccine efficacy and immunogenicity thresholds are derived, and the minimum level of adult vaccination required for eradication of targeted types is determined. Results We demonstrate that eradication of targeted types is indeed feasible, although the burden of coverage for a childhood-only vaccination program may be high. However, if a small, but non-negligible, proportion of eligible adults can be vaccinated, then the possibility of eradication of targeted types becomes much more favourable. We provide a threshold for eradication in general communities and illustrate the results with numerical simulations. We also investigate the effects of suboptimal efficacy and immunogenicity and show that there is a critical efficacy below which eradication of targeted types is not possible. If eradication is possible, then there is a critical immunogenicity such that even 100% childhood vaccination will not eradicate the targeted types of the virus and must be supplemented with voluntary adult vaccination. However, the level of adult vaccination coverage required is modest and may be achieved simply by removing the cost burden to vaccination. Conclusion We recommend that provincial healthcare programs should pay for voluntary adult vaccination for women aged 14–26. However, it should be noted that our model results are preliminary, in that we have made a number of simplifying assumptions, including a lack of age-dependency in sexual partner rates, a lack of sexual activity outside of the vaccine age-range among females and a uniform age of sexual debut; thus, further work is desired to enhance the external generalisability of our results.</p

Health issues associated with increasing use of "crack" cocaine among female sex workers in London

Objectives: To document changes in "crack" cocaine use in the sex industry in London, and to assess health risks associated with the drug. Design: Two serial cross sectional surveys. Subjects: Sex workers interviewed in 1989–9 and 1995–6. Main outcome measures: Self reported use of crack cocaine; clinical history of sexually transmitted infection and pregnancy, clinical outcomes. Results: The proportion of women reporting crack use increased significantly from 22/193 (11%) in 1989–91 to 48/143 (34%) in 1995–6. Women in all the main prostitution sectors reported crack use. Crack users had been working in prostitution for longer, were more likely to have worked on the streets, to inject drugs, and to have a partner who injected. Crack use was associated with termination of pregnancy and with hepatitis C infection. The association with hepatitis C was partially explained by confounding with injecting drug use. Conclusions: Crack use is more common and less problematic than clinical presentation suggests. Use has increased over the past decade, and is associated with hepatitis C infection and termination of pregnancy. It is possible that crack use facilitates hepatitis C transmission due to oral lesions from smoking. Crack use can be difficult to identify because of the stigma of being labelled a "crack whore," therefore information on crack might usefully be integrated into general health promotion material on drugs and safer sex. Key Words: "crack" cocaine; female sex workers; Londo