Serial interval, basic reproduction number and prediction of COVID-19 epidemic size in Jodhpur, India (preprint)

ABSTRACT

Background: Understanding the epidemiology of COVID19 is important for design of effective control measures at local level. We aimed to estimate the serial interval and basic reproduction number for Jodhpur, India and to use it for prediction of epidemic size for next one month. Methods: Contact tracing of SARSCoV2 infected individuals was done to obtain the serial intervals. Aggregate and instantaneous R0 values were derived and epidemic projection was done using R software v4.0.0. Results: From among 79 infector infectee pairs, the estimated median and 95 percentile values of serial interval were 5.98 days (95% CI 5.39 to 6.65) and 13.17 days (95% CI 11.27 to 15.57), respectively. The overall R0 value in the first 30 days of outbreak was 1.64 (95% CI 1.12 to 2.25) which subsequently decreased to 1.07 (95% CI 1.06 to 1.09). The instantaneous R0 value over 14 days window ranged from a peak of 3.71 (95% CI 1.85 -2.08) to 0.88 (95% CI 0.81 to 0.96) as on 24 June 2020. The projected COVID-19 case-load over next one month was 1881 individuals. Reduction of R0 from 1.17 to 1.085 could result in 23% reduction in projected epidemic size over the next one month. Conclusion: Aggressive testing, contact-tracing and isolation of infected individuals in Jodhpur district resulted in reduction of R0. Further strengthening of control measures could lead to substantial reduction of COVID19 epidemic size. A data-driven strategy was found useful in surge capacity planning and guiding the public health strategy at local level.