R0 is a mathematical term that represents the number of new infections that could stem from a single case The R0 value indicates how contagious an infectious disease is and hence it is an important marker to study the progression of a disease As an infection is transmitted to new people, it reproduces itself. Therefore, R0 is also referred to as the reproduction number R0 indicates the average number of people who contract a contagious disease from an infected person It specifically applies when everyone in the population is completely vulnerable to the disease That is, people in a population where no one has been vaccinated, no one has had the disease before and when there’s no way to check the spread of the disease Using the R0 value, the transmission rate of a disease or its decline can be calculated If R0 is less than 1, each existing infection causes less than one new infection. In this case, the disease will decline and eventually die out If R0 equals 1, each existing infection causes one new infection. The disease will stay alive and stable, but there won’t be an outbreak or an epidemic If R0 is more than 1, each existing infection causes more than one new infection. The disease will be transmitted between people, and there may be an outbreak or epidemic R0 of a disease is calculated on the basis of its infectious period, mode of transmission, and contact rate If the disease has a longer infectious period, then it is more likely that an infected person can transmit it to other people So the R0 value will be higher if it has a longer infectious period The disease will be transmitted quickly, if an infected person comes in contact with people who aren’t infected or vaccinated. Therefore, high contact rate will result in a higher R0 value The mode of transmission also contributes to the R0 value For example, airborne illnesses are transmitted the fastest and easiest. Therefore, they tend to have a higher R0 value than those spread through direct contact Countries have been trying to find out the R0 value of COVID-19 as a metric to find out the transmission rate of the virus But the R0 value is not a constant number The estimates can vary by location, depending on factors such as how often people come into contact with each other and the efforts taken to reduce viral spread Preliminary studies estimated a global R0 value for COVID-19 to be between 2 and 3.This means each infected person has spread the virus to an average of 2 to 3 people But some recent studies suggest COVID-19 has an even higher R0 value According to Institute of Mathematical Sciences, Chennai, between April 13 and May 10, the R0 value of COVID-19 in India remained steady at 1.29 At the beginning of lockdown, it was 1.83 An R0 of 1 and above tends towards exponential growth whereas an R0 of below 1 tends towards the end of the outbreak Therefore, it is important to is keep the R0 value below 1

• published: 20 May 2020
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