Measles in Canada: modelling outbreaks with variable vaccine coverage and interventions.

Area of Science:

• Epidemiology
• Mathematical Modeling
• Public Health

Background:

• Global measles incidence is rising, posing a risk to countries like Canada, which previously had elimination status.
• While most Canadians are vaccinated, pockets of low vaccination coverage exist, increasing vulnerability to imported measles cases.
• Measles elimination status in Canada is threatened by imported cases, particularly in communities with suboptimal vaccination rates.

Purpose of the Study:

• To model potential measles outbreaks in Canada following importation.
• To assess the impact of varying vaccination coverage levels and public health interventions on outbreak dynamics.
• To provide a tool for projecting measles outbreak size and duration in local Canadian scenarios.

Main Methods:

• Development of a stochastic Susceptible-Exposed-Infectious-Recovered (SEIR) model.
• Simulation of measles importation into Canada under diverse scenarios.
• Comparison of model-generated outbreak data with real-world measles outbreak reports.

Main Results:

• Community-level measles outbreaks are controllable at or above 85% vaccination coverage with interventions.
• Above 95% vaccination coverage, 99% of measles introductions do not lead to outbreaks.
• Outbreak size and duration are significantly influenced by vaccination coverage, community size, and intervention strength, with outbreaks often lasting under 60 days.

Conclusions:

• The developed model aids in bridging global measles risks to local Canadian contexts.
• The model projects the potential duration and size of measles outbreaks upon importation into Canada.
• This projection capability can inform public health responses and communicate measles-related risks to the Canadian public.