  We present a System Dynamics (SD) model of the Covid-19 pandemic spread in
India. The detailed age-structured compartment-based model endogenously
captures various disease transmission pathways, expanding significantly from
the standard SEIR model. The model is customized for India by using the
appropriate population pyramid, contact rate matrices, external arrivals (as
per actual data), and a few other calibrated fractions based on the reported
cases of Covid-19 in India. Also, we have explicitly modeled, using independent
time-variant levers, the effects of testing, contact tracing, isolating
Covid-positive patients, quarantining, use of mask/better hygiene practices,
social distancing through contact rate reductions at distinct zones of home(H),
work(W), school(S) and other(O) locations. Simulation results show that, even
after an extended lock-down, some non-trivial number of infections (even
asymptomatic) will be left and the pandemic will resurface. Only tools that
work against the pandemic is high rate of testing of those who show Covid-19
like symptoms, isolating them if they are positive and contact tracing all
contacts of positive patients and quarantining them, in combination with use of
face masks and personal hygiene. A wide range of combination of effectiveness
of contact tracing, isolation, quarantining and personal hygiene measures help
minimize the pandemic impact and some imperfections in implementation of one
measure can be compensated by better implementation of other measures.
