How much of SARS-CoV-2 Infections is India detecting? A model-based estimation

Srinivas Goli; K.S. James

Researchers from the University of Gottingen used age-specific infection fatality rates from a study published in The Lancet Infectious Diseases journal 5,1 to estimate the total number of infections. The details of Bommer and Vollmer (2020) model are presented elsewhere 5 . We have adjusted the age-specific infection fatality rates presented in the Lancet with the age distribution of the population of India and 13 states which have more than 100 confirmed cases as on 8 th April. The Lancet study reported perfect ascertainment between observed and estimated cases in the age group 50-59 years. We apply the infection fatality rate of this age group to all ages assuming infection attack rate is uniform for population across the agegroups in India. The number of infections is estimated as the number of deaths till April, 08, 2020 divided by the adjusted infection fatality rate. Based on the global evidence, we assumed that the mean duration between the onsets of symptoms to deaths is 14 days. Thus, it yields the total number of infections two weeks prior to April 8. The detection rate is estimated as the number of confirmed cases divided by the estimated number of infections. Further, by taking data from reports of the ICMR, we have also adjusted the detection rates with the sum of the difference in the rate of change in testing done on a daily basis to derive a more realistic figure of the total number of infections (confirmed + undetected infections) for India as of April 8.