On the parameterization of mathematical models of infectious disease transmission structured by age at the start of the epidemic spread

Estimation of transmission and contact rate parameters among individuals in different age groups is a key point in the mathematical modeling of infectious disease transmission. Several approaches exist for this task but, given the complexity of the problem, the obtained values are always approximate estimations that hold in particular conditions. Our goal is to contribute to this task in the event of an emerging disease. We propose a methodology to estimate the contact rate parameters from the fraction of the incidence reported in each age group at the beginning of the epidemic spread. Working with an age-structured SIR model, we obtain an equation that relates the contact parameters to various epidemiological quantities that could be accessible through different sources. We apply the method to obtain information about the contact structure by age during the COVID-19 epidemic spread in Greater Buenos Aires (Argentina) in 2020. As we have the fractions of reported incidence by age but only rough estimations of other quantities involved in the method, we define several epidemiological scenarios based on various hypotheses. Using the different sets of contact parameters obtained, we evaluate control strategies and analyze the dependence of the results on our assumptions. The proposed method could be useful to obtain a fast first insight of a new emergent disease at the beginning of epidemic spread using the accessible information.