Data discrepancy

A couple of studies use naturally occurring control groups—passengers in the Diamond Princess and those who returned to Wuhan after foreign travel—and COVID-19 mortality data to calculate the Infection Fatality Ratio and with that work backwards to arrive at the true caseload in a country, which is far higher than the official numbers put out by countries.

- R. RAMACHANDRAN

THE LACK OF KNOWLEDGE ABOUT THE TRUE number of COVID-19 positive cases in any country or region seems to be the elephant in the room in the ongoing COVID-19 pandemic. The severity of any epidemic has two aspects: one, how infectious or contagious the causative pathogen—in this case, the coronavirus SARS-CoV-2—of the disease is; and, two, how dangerous it is; that is, how many in a cohort group of COVID-19 patients the disease will kill, and equivalently, what the chances are that a person who becomes positive for the virus will eventually die.

A measure of the first is given by a parameter called the Basic Reproduction Number, denoted by R0 (pronounced “R-nought”), which is the number of people that an infected person is likely to transmit the infection to. In a new and growing epidemic, R0 is usually greater than 1; that is, one person is likely to infect more than one person, and the secondary infected persons will each go on to infect R0 more number of persons, leading to an exponential growth in the number of infected persons.

R0 is not a fixed number; it is a dynamic parameter that can be brought down by reducing the chances of the infection being transmitted from person to person by measures such as physical distancing among people, hygienic practices such as regular washing of hands, isolation of infected persons, self-quarantine and so on. Once R0 becomes less than 1, the infection spread will decline and eventually die out. Scientists estimate R0 by constructing models of transmission of infection in a given social setting.