Effective Reproduction Number and Dispersion under Contact Tracing and Lockdown on COVID-19 in Karnataka

We study the effectiveness and limitations of contact-tracing, quarantine, and lockdown measures used in India to control the spread of COVID-19 infections. Using data provided in the media bulletins of Government of Karnataka we observe that the so called $$20-80$$ rule holds for secondary infections and classify them into clusters. Using a mixture of Poisson with Gamma model we establish that clusters show variation in deceased rates ( $$ 0\%-17.31 \%$$ ), low reproduction numbers ( $$0.21-0.77$$ ), small dispersion( $$0.06-0.18$$ ), and that super-spreading events can occur. Further, migration due to relaxation in lockdown is unlikely to be the sole cause of recent surge. The methodology presented is universal in nature and can be applied whenever such precise data is available.