For the most comprehensive information on measles (which is experiencing a resurgence in outbreaks in parts of the US and Canada), please see:
Ontario: https://www.publichealthontario.ca/en/Diseases-and-Conditions/Infectious-Diseases/Vaccine-Preventable-Diseases/Measles
Canada: https://www.canada.ca/en/public-health/services/laboratory-biosafety-biosecurity/pathogen-safety-data-sheets-risk-assessment/measles-virus.html
We provide a dashboard to illustrate to the public the possible evolutions of measles outbreaks for the population of 0-9 years old in the Wellington-Dufferin-Guelph PH (which encompasses approximately 33,500 kids, attending daycare and school on a regular basis). This model is a compartmental model with susceptible (S), Exposed (E), isolated (L), traced isolated and vaccinated post-exposure (VL), vaccinated (V) and Recovered (R). We follow the classic quantification of the relation between the initial reproduction number (R0) and the transmission rate between a susceptible and an infected individual, where the transmission rate is a product of contact rates and probability of transmission of measles per contact.
The dashboard allows for customization of “Contact Rate” between kids in this age range and assume a 0.9 probability of transmission from an infected individual to a susceptible one per contact (measles has an estimated initial reproduction number of 8-12).
The model assumes that the overall coverage in the children population is 0.9 with a vaccine efficacy (typically MMR-type) of 0.95%.
The model assumes that “Contact Tracing” takes place once an infected case in the community is identified – tracing of exposed individuals is important, as unvaccinated exposed can be offered vaccination post-exposure up to 6 days. It is known that the vaccine efficacy in these cases varies, depending on the number of days since exposure and the type of vaccine [MMR dose 1 is given within 3 days of exposure (efficacy 92%-95%), IG PEP is given within 6 days of exposure (efficacy 65%-90%) ]. Here we represent it as “Vaccine Efficacy post-Exposure”.
The assumes that all traced individuals will agree to either just isolate (L) post-exposure or isolate & vaccinate post-exposure (VL); it further assumes that non-traced individuals become infected and (given the weight times for family doctors and shortages in primary care coverage) there will be a variable “Isolation post-symptoms” for each infected child.
The model assumes the recovery period is 7-10 days.
A few scientific references:
- http://10.1371/journal.pone.0167160
- Dynamics of Vaccination Strategies via Projected Dynamical Systems – https://link.springer.com/article/10.1007/s11538-006-9173-x
- Age-specific measles mortality during the late 19th–early 20th centuries – https://pmc.ncbi.nlm.nih.gov/articles/PMC9150958/