COVID-19: Understanding R0 and Rt

In an interview with the Star newspaper, Prof Datuk Dr Awang Bulgiba Awang Mahmud and Prof Dr Sanjay Rampal explain the methods used to measure the spread of an infectious disease.

Prof Awang said that while the R value was an important indicator of whether a country was safe from Covid-19, it was not the only one. Other indicators include the country’s capacity to cope with the disease, and the trend in the number of new cases and discharged individuals in comparison with the number of new infections.

The R0 or R-naught is the initial reproduction number of the virus at the beginning of the pandemic. Rt refers to the reproduction number at a particular point in time.

Rt value means the effective reproduction number. An Rt of less than 1.0 means the infection is not spreading. It means that the number of people being infected on average will get fewer over time and if this situation persists, the disease will eventually die out.

An Rt value above 1.0 means the virus is spreading fast

An Rt of 1.0, meant that a disease was endemic and would persist over time, such as dengue.

On Sept 8, he showed in a tweet how the Rt value had jumped to 1.72, following the emergence of large clusters in Sabah and Kedah. Only two weeks before, the Rt value was 0.72.

Prof Sanjay said in general, the R0 value of the COVID-19 virus was estimated to be about 5.7 or 5.8.

This means that one COVID-19 infected person could on an average pass the disease on to five to six people if the virus is allowed to spread without any form of public health intervention.

Prof Sanjay explains that the infectiousness of the virus depends on the agent of the virus and the environment.

He said that various factors, he added, affected the Rt value, such as the mutation of the Covid-19 virus and the intensity and compliance with public health interventions.

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