Research Projects and Contributions

Modeling the impact of interventions against Human Papillomavirus (HPV) related diseases

Background: Should we vaccinate girls and boys against HPV, a sexually transmitted infection that causes cervical cancer? This question has raised great debate in Canada, and in other developed countries. Since 2007, my research team has been developing and using mathematical models to predict the effectiveness and cost-effectiveness of HPV vaccination programs and, importantly, translating results for use in policy decisions by working in partnership with guideline-making bodies. We were the first to publish results from a mathematical model, which examined the potential health and economic impact of vaccinating against HPV in Canada. Furthermore, we developed the first calibrated individual-based transmission-dynamic model of HPV (HPV-ADVISE). Key findings published in the American Journal of Epidemiology, Canadian Medical Association Journal, Journal of Infectious Diseases, Vaccine and Sexually Transmitted Infection suggest that: 1) 324 girls would have to receive the HPV vaccine to prevent 1 case of cervical cancer, assuming vaccination offers lifelong protection, 2) vaccinating girls against HPV is likely to be cost-effective, 3) unless screening is modified, the treatment costs saved through vaccination will be insignificant compared to the cost of immunization, 4) vaccine effectiveness will likely  be higher for HPV-6/11/18 than for HPV-16, the type responsible for the greatest burden of disease, and 5) given the important predicted herd immunity impact of vaccinating girls under moderate to high vaccine coverage, the incremental gains of vaccinating boys are limited.

Significance: The work produced by our team has helped inform policy decisions on HPV vaccination at the provincial, federal and international level. Furthermore, findings were presented to different government organizations (Canadian Immunization Committee (CIC), National Advisory Committee on Immunization (NACI), Comité sur l'immunisation du Québec (CIQ), and U.S. Centers for Disease Control and Prevention (CDC)). The research has benefited from important media coverage (internet, television, newspapers, radio, magazines), which has helped inform the public about the potential impact of HPV vaccination. Since our first HPV modeling publication (2007), our papers on the subject have been cited 250 times.

Measuring the effect of exposure to Varicella on Zoster incidence

Background: Varicella zoster virus (VZV) produces two different diseases: varicella (primary infection) and zoster (reactivation of VZV). In Brisson et al., we were the first to present strong evidence which confirmed the hypothesis that exposure to varicella boosts immunity to zoster. That is, that exposure to VZV protects against zoster.

Significance: These findings had and still have major implications for varicella vaccination: by reducing varicella cases (and thus the opportunity of exposure to VZV), mass infant immunization could increase the incidence of zoster in individuals who have not been vaccinated. The study supported a re-evaluation of varicella vaccination taking into account its possible impact on zoster. The research was selected as one of the 100 top Science stories of 2002 by Discover magazine and has over 150 citations.

Modeling the effectiveness and cost-effectiveness of VZV Vaccination

Background: In a series of publications between 2000 and 2010 we estimated, using dynamic models, the effectiveness and cost-effectiveness of routine childhood varicella vaccination. We were the first to include the impact of vaccination on zoster incidence. Results showed that varicella vaccination with one or two doses will likely provoke an increase in zoster incidence. Furthermore, it is unclear whether 1- or 2-dose varicella vaccination is cost-effective in Canada given important uncertainties regarding long-term varicella vaccine efficacy and the potential increase of zoster.

Significance: This research was instrumental in recommendations regarding the routine administration of varicella vaccination in Canada, the U.S., Australia and Europe. Furthermore, over the past ten years, these results have been presented to different government organizations (Canadian Immunization Committee (CIC), National Advisory Committee on Immunization (NACI), and Comité sur l'immunisation du Québec (CIQ)). Importantly, the findings have been an impetus for long term surveillance of zoster in the U.S., where routine childhood varicella vaccination was introduced in 1995. Our papers on VZV vaccination have been cited 900 times.

Evaluating the impact of methodological choices when modeling the effectiveness and cost-effectiveness of immunization programs:

Background: The bulk of economic evaluations of vaccination use models, which do not take into account the unique complexities of infectious diseases. In a series of papers and presentations, we quantified the impact of ignoring effects such as herd immunity when assessing the cost-effectiveness of vaccination programs and how uncertainty of modeling results should be addressed and presented.

Significance: Results were used to clarify a number of misconceptions that are common in the literature regarding the impact of herd immunity on model predictions and to provide guidelines for the economic evaluation of immunization programs. Our methodological papers have been cited over 160 times since 2003.

Estimating the psychosocial impact and the Quality-Adjusted Life-Years (QALY) lost associated with Rotavirus, Herpes zoster and HPV-related diseases

Background: Although QALYs are the most widely used measure of health benefit in cost-effectiveness analyses, very few data were available to quantify the QALYs lost associated with rotavirus, herpes zoster, post herpetic neuralgia (PHN) and HPV-related diseases. In addition, the few estimates available in the literature were obtained from cross-sectional studies conducted among small convenience samples of patients and were thus likely to be biased. In a series of recent papers and presentations, we quantified the psychosocial impact and the QALYs lost associated with these diseases.

Significance: Findings have only recently been published. However, they have been used in cost-effectiveness analysis of vaccination against rotavirus, herpes zoster and HPV in countries across Europe, and in Australia, Canada and the U.S.

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