Optimal COVID-19 epidemic control until vaccine deployment

Ramses Djidjou-Demasse; Yannis Michalakis; Marc Choisy; Micea T. Sofonea; Samuel Alizon

Broadly speaking, there are two main ways to halt the spread of the epidemics. The first one is through natural immunisation: once a proportion 1−1/R 0 of the population has been infected (where R 0 is the basic reproduction number), a 'herd immunity' develops and the epidemic starts to decrease [1] . Note that this herd immunity threshold is lower than the 'worst-case scenario', i.e. the epidemics final size if no containment measure is implemented [13] . The second option is to achieve population immunisation through vaccination. The threshold to have the epidemics decrease remains the same, but the cost in terms of mortality can be much lower. These options have been investigated by the WHO Collaborating Centre for Infectious Disease Modelling in two reports [7, 24] . The first report explores the effect of an on/off triggering of 5 types of non-pharmaceutical interventions, whereas the second report compares a containment strategy to a suppression strategy, while factoring in indirect costs of implementing the strategy. Other models have explored the efficiency of contact tracing to mitigate the epidemics [11, 12] .