Impact of nonpharmacological interventions on COVID-19 transmission dynamics in India.

Patel, Purvi; Athotra, Aditya; Vaisakh, T P; Dikid, Tanzin; Jain, Sudhir Kumar

Background As of May 4, 2020, India has reported 42,836 confirmed cases and 1,389 deaths from COVID-19. India's multipronged response included nonpharmacological interventions (NPIs) like intensive case-based surveillance, expanding testing capacity, social distancing, health promotion, and progressive travel restrictions leading to a complete halt of international and domestic movements (lockdown). Objectives We studied the impact of NPI on transmission dynamics of COVID-19 epidemic in India and estimated the minimum level of herd immunity required to halt it. Methods We plotted time distribution, estimated basic (R0) and time-dependent effective (Rt) reproduction numbers using software R, and calculated doubling time, the growth rate for confirmed cases from January 30 to May 4, 2020. Herd immunity was estimated using the latest Rtvalue. Results Time distribution showed a propagated epidemic with subexponential growth. Average growth rate, 21% in the beginning, reduced to 6% after an extended lockdown (May 3). Based on early transmission dynamics, R0was 2.38 (95% confidence interval [CI] =1.79-3.07). Early, unmitigated Rt= 2.51 (95% CI = 2.05-3.14) (March 15) reduced to 1.28 (95% CI = 1.22-1.32) and was 1.83 (95% CI = 1.71-1.93) at the end of lockdown Phase 1 (April 14) and 2 (May 3), respectively. Similarly, average early doubling time (4.3 days) (standard deviation [SD] = 1.86) increased to 5.4 days (SD = 1.03) and 10.9 days (SD = 2.19). Estimated minimum 621 million recoveries are required to halt COVID-19 spread if Rtremains below 2. Conclusion India's early response, especially stringent lockdown, has slowed COVID-19 epidemic. Increased testing, intensive case-based surveillance and containment efforts, modulated movement restrictions while protecting the vulnerable population, and continuous monitoring of transmission dynamics should be a way forward in the absence of effective treatment, vaccine, and undetermined postinfection immunity.