Spread In The Community

India has acknowledged that the Covid-19 pandemic is now in the community transmission stage. How is this stage defined, and what are its implications? What changes in strategies to contain the spread?

Anuradha Mascarenhas & Amitabh Sinha

In the third wave of the coronavirus epidemic, India has acknowledged that the disease is now in the community transmission stage. While it is no more than a statement of the obvious, and has little operational implication at this stage of the epidemic, this acknowledgment has attracted attention because this is the first time India has officially done so.

What it means

In all regions except the origin of the outbreak, the virus is introduced into the population by travellers. In the initial stages of an epidemic, all further transmissions of the disease can be linked, directly or through a chain, to these travellers. But after some time, as more and more people get infected, they pass on the virus to many more, several of whom are never detected because they might be asymptomatic or did not get tested. But even these undetected cases would have transmitted the disease to others. Very soon, it results in a situation where the chain of infections can no longer be traced to the original travellers, and most of the infections become locally acquired. It is this stage of the epidemic that is classified as one of community transmission.

In simple terms, it is a stage where it becomes difficult to establish the chain of infections, or determine who infected whom. This has implications for deciding containment strategies and response measures to deal with the epidemic.

Community transmission is the final stage of classification of the epidemicon this basis.

The World Health Organization (WHO) has three more classifications ahead of community transmission - no active cases, sporadic cases and cluster of cases. If no new cases are detected in 28 days, a countryor region is said to have no new active cases. A situation where all the known infections in the previous two weeks can be linked to an imported case is classified as being in the second category.