Why lockdown? Simplified arithmetic tools for decision-makers, health professionals, journalists and the general public to explore containment options for the novel coronavirus

Gerry Killeen; Samson Kiware

Furthermore, elimination may only be sustained by comprehensively containing case importation from outside the country ( Figure 2G and H). Preventing reintroduction requires isolation of all incoming travellers, except those coming from countries that may be certified as free of local transmission by WHO in the future, to achieve 100% prevention of onward local transmission ( Figure 1 ). Even 90% containment of imported cases seems unlikely to protect the country against reintroduction of the virus and re-initiation of the epidemic ( Figure 2G and H). Tanzania therefore did the right thing by isolating all inbound travelers since March 23 rd (over 600 so far) for two weeks following their arrival). However, for such importation containment measures to effectively exclude new cases from a COVID-free Tanzania in the future, isolation periods may need to be extended to three weeks. 2, 3, 5, 7, 69, 70, 78 However, it is also notable that all the scenarios in figure two, except for panels G and H, assume 100% effective containment of imported cases. It is therefore clear that local transmission must be eliminated before such rigorous control of inbound travellers can usefully protect the country against reintroduction.