Risk of Influenza Infection with Low Vaccine Effectiveness

Speaker: Dr. Seyed M. Moghadas

Abstract: Low vaccine-effectiveness is a factor undermining efforts to improve strategies and uptake of influenza vaccination. Aiming to prevent disease transmission, vaccination may influence the perceived risk-of-infection and, therefore, alter the individual-level behavioural responses, such as the avoidance of contact with infectious cases. We asked how the avoidance behaviour of vaccinated individuals changes disease dynamics, and specifically the epidemic size, in the context imperfect vaccination. In this talk, I will present the outcomes of an agent-based simulation model, which was developed to address the proposed question. The model was parameterized with published estimates and relevant databases for population demographics and agent characteristics in Canada. Considering the rate of virus mutations and vaccine efficacy, we evaluated the per-contact risk-of-infection and estimated the epidemic size. Our results show that vaccination could lead to a larger epidemic size if the level of avoidance behaviour in vaccinated individuals reduces below that of susceptible individuals. We found that the risk-of-infection in vaccinated individuals follows the pattern of age-dependent frailty index of the population, and may reach, or even exceed, the risk-of-infection in susceptible individuals for older age groups. While presenting the results, I will also discuss the importance of our findings for improving vaccination strategies.