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Virus transmission term ‘R0’

Date: 10 April 2020 Tags: Disaster & Disaster Management


While billions of people around the world are currently living under a lockdown due to the coronavirus pandemic, researchers are still in the process of understanding the nature of its transmission. In these studies, the mathematical figure ‘R0’, which indicates how fast an infection is spreading, is considered essential.



Numerous studies are being done to understand how contagious the virus is. This is important as it helps governments make more informed decisions on how to lift lockdown measures while safeguarding lives.



  • R0 (pronounced “R-naught”) is the rate at which a virus is transmitted. Also called the basic reproduction number, it indicates the average number of people who will contract the virus from a person who has already been infected, in a population that does not have immunity for the said disease.

  • R0 is the division of the number of new infections by the number of existing infections, or the average number of new infections over an infectious period (R0= new infections/existing infections). The higher the R0, the more contagious the infection.

  • To illustrate with an example, if the number of people diagnosed with a disease increases from four to eight in two days, it is likely to increase to 16 two days later, or in four days from the start. This makes the R0 two.

  • When the R0 is 1, it means the number of infected persons in a population is constant. For every person who is cured of the disease or dies due to it, there will be one fresh case in the population.

  • By this logic, the ideal scenario is when the R0 is below 1. This means the infection is transmitted to fewer people. When such a rate is maintained over a considerable period of time, the disease is eradicated.

  • Disease transmission is not fixed, and the rate can be reduced by pharmaceutical interventions (like vaccines) or non-pharmaceutical interventions (screenings, lockdowns), or both.

  • Once such measures are put in place, contagiousness is measured in terms of Rt, or the actual rate of transmission at time t. The same strategy has been used in the past for eliminating diseases such as polio and smallpox.

  • While many studies have differed in their conclusions, the World Health Organization (WHO) has estimated the R0 for coronavirus at 1.4 to 2.5. In China’s Wuhan, where the disease originated, lockdown measures brought the Rt (effective rate) down to 0.3, thus significantly slowing the number of new infections.

  • Governments around the world which have enforced such measures are hoping to follow the same path, although experts fear a second wave of infections once lockdowns are lifted.

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