The Wilson-Rathish Index (WRI): A Simple Index to Facilitate Decision Making on Containment Measures in COVID-19

Abstract

The global response to the ongoing COVID-19 pandemic has been characterised by differing population level strategies by different levels of ‘lockdowns’ including movement restrictions, physical distancing aimed at interrupting transmission cycles and slowing the spread in different countries. The initiation and lifting of lockdowns often seem to lag behind in terms of good quality evidence. We conducted as a retrospective cohort study involving the populations of the country of South Korea, the city of New York in the United States of America, and the state of Kerala in India. Publicly available data on number of newly diagnosed COVID-19 cases per day as well as the number of COVID-19 tests done per day in these 3 geographical areas were accessed from official government data sources as well as data sharing websites. With the CDC’s recommendation of incubation period for COVID-19 to be taken as 14 days, we calculated a daily 14 day average of the C/T ratio, termed as 14DACT consisting of 14 day averages of the preceding 14 days. We also calculated the total average of the C/T ratio from which time the data was made available and termed it TDACT which consisted of the total average from day 1 of available data to date. Finally a daily Wilson-Rathish Index (WRI) was calculated as that day’s 14DACT divided by the TDACT as on that day. We hypothesise that a WRI above 1 indicates that containment measures are inadequate and more rigorous lockdown measures should be continued until it drops below 1. A WRI below 1 indicates that the lockdown measures were adequate and that some form of relaxation may be attempted with a close watch on serial prospective WRI, with a lockdown to be re-initiated if the WRI ever crosses 1. Serial monitoring of WRI may aid this process which is currently being done based on only reported number of cases, that does not take into account the number of tests performed or the transmission rates in the preceding incubation period of 14 days.