  A pandemic caused by a new coronavirus (COVID-19) has spread worldwide,
inducing an epidemic still active in Argentina. In this chapter, we present a
case study using an SEIR (Susceptible-Exposed-Infected-Recovered) diffusion
model of fractional order in time to analyze the evolution of the epidemic in
Buenos Aires and neighboring areas (Regi\'on Metropolitana de Buenos Aires,
(RMBA)) comprising about 15 million inhabitants. In the SEIR model, individuals
are divided into four classes, namely, susceptible (S), exposed (E), infected
(I) and recovered (R). The SEIR model of fractional order allows for the
incorporation of memory, with hereditary properties of the system, being a
generalization of the classic SEIR first-order system, where such effects are
ignored. Furthermore, the fractional model provides one additional parameter to
obtain a better fit of the data. The parameters of the model are calibrated by
using as data the number of casualties officially reported. Since infinite
solutions honour the data, we show a set of cases with different values of the
lockdown parameters, fatality rate, and incubation and infectious periods. The
different reproduction ratios R0 and infection fatality rates (IFR) so obtained
indicate the results may differ from recent reported values, constituting
possible alternative solutions. A comparison with results obtained with the
classic SEIR model is also included. The analysis allows us to study how
isolation and social distancing measures affect the time evolution of the
epidemic.
