Estimation of country-level basic reproductive ratios for novel Coronavirus (COVID-19) using synthetic contact matrices

Joe Hilton; Matt J Keeling

A 2017 study by Prem et al. estimated contact patterns for 152 countries based on social and demographic data. These are in the form of matrices whose entries correspond to the expected total number of agestratified contacts per day for individuals belonging to each of 16 5-year age classes [3] . These estimated contact matrices are publicly available as supplementary material attached to Prem et al.'s paper. Here we use the estimated social contact matrix for China to define the early age-structured transmission dynamics; this is formed from the country-specific social contact matrix k and a vector of age-specific susceptibilities z -whose entries scale the risk of transmission from contact with infected individuals to susceptible individuals of each age class. Based on age-structured data from the outbreak in China, we can estimate z. We then combine z with Prem et al.'s estimates of the contact matrices in the other 151 countries to generate an estimate of an age-structured transmission structure for each of those countries. The basic reproductive ratio can then be estimated from these transmission structures to give us an approximation of the spreading potential of a COVID-19 outbreak in each of these countries.