Abhijit Paul, Samrat Chatterjee, Nandadulal Bairagi*
The pandemic disease Covid-19 caused by SARS-COV-2 has established itself as the most devastating disease in the history of infectious disease, affecting 216 countries/territories across the globe. Policies like social distancing and lockdown were adopted to tackle the spreading of the disease. The disease is still not under control, but many countries have withdrawn the lockdown and going through phase-wise unlock-ing process. The removal of movement restriction causes free circulation of the disease mostly through the undetected class. The present study is an attempt to understand and estimate the possible epidemic burden during the unlock phase in the presence of the undetected class. Through a modified SEIR model, we focus our study on India and the USA, where the epidemic curve is still growing and the unlock process has started. We estimated the parameter values for both the countries using available data and used them to calculate the basic reproduction number. We also performed a global sensitivity analysis to search for the most sensitive parameters which can significantly change the dynamics of the disease. We observed that the use of repurposing drugs may further decrease the infected cases and help the disease controlling process. Our results emphasize on the implementation of 3T principles, trace, test, and treat, to contain the epidemic. The significance of large-scale testing in restricting the spread of infection during the unlock phase is evident for both India and the USA though they have different socio-economic conditions.