Incubation Period and Reproduction Number for Novel Coronavirus 2019 (COVID-19) Infections in India

Novel coronavirus 2019 (COVID-19) rapidly spread from China to other parts of the world. Knowledge of incubation period and reproduction number is important in controlling any epidemic. The distribution of these parameters helps estimate the epidemic size and transmission potential of the disease. We estimated the incubation period and reproduction number of COVID-19 for India utilizing data reported by the Ministry of Health and Family Welfare, Government of India, and data in public domain. The mean incubation period seems to be larger at 6.93 (standard deviation = +/- 5.87, 95% confidence interval [CI] = 6.11-7.75), and 95th percentile estimate for best fit normal distribution is 17.8 days. Weibull distribution, the best fit for the reproduction number estimated pre lockdown reproduction number as 2.6 (95% CI = 2.34-2.86) and post lockdown reduced to 1.57 (95% CI = 1.3-1.84) implying effectiveness of the epidemic response strategies. The herd immunity is estimated between 36% and 61% for R(0)of 1.57 and 2.6, respectively.