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

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).

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.

We plotted time distribution, estimated basic (R₀) and time-dependent effective (R_t) 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 R_tvalue.

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 R_t= 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 R_tremains below 2.

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.