Countries should aim to lower the reproduction number R close to 1.0 for the short-term mitigation of COVID-19 outbreaks

Michael E. Hochberg

where â„›0 is the basic reproductive number at the start of an outbreak (15) and â„›C is the level of â„› that suppression or mitigation tactics strive to achieve in order to reduce the burden of an outbreak or meet specific objectives. Note that with the possible exception of a given country adopting or modifying measure packages engaged in other countries, governments do not know beforehand exactly what a given set of measures will achieve in terms of precise reductions in â„›0 and the corresponding impacts on the outbreak. Many countries -for example, Italy, France, Spain, Germany and the United States -are currently in the second (suggested mitigation measures, e.g., social distancing, quarantining...) or third (enforced lockdowns) phase of this simple suite of strategies. A successful step 2 that actually results in â„›C<1.0 may take the country directly to step 4, or possibly step 5, the latter which also seeks â„›C<1.0, but does so through less socially burdensome measures, such as the introduction of repurposed drugs and vaccination.