FOR THE first SARS pandemic in 2003, scientists estimated the original R0 to be around 2.75. A month or two later, the effective R0 dropped below 1, thanks to the tremendous effort that went into intervention strategies, including isolation and quarantine activities.
Scientists use R0 – the reproduction number – to describe the intensity of an infectious disease outbreak. R0 estimates have been an important part of characterizing pandemics or large publicized outbreaks, including the 2003 SARS pandemic, the 2009 H1N1 influenza pandemic and the 2014 Ebola epidemic in West Africa. ‘It’s something epidemiologists are racing to nail down about SARS-CoV-2, the virus that causes COVID-19.’
Since SARS-CoV-2, the virus that causes COVID-19 is a sister clade of SARS, it is extremely useful to simply refer to the bug as SARS2. In fact much of what was learnt during the first epidemic should be applied to the latest outbreak. For example, SARS was transmissible via respiratory and bodily fluid. Until evidence is provided to the contrary, one must assume this to also be the case with SARS2.
In the 1950s, epidemiologist George MacDonald suggested using R0 to describe the transmission potential of malaria. He proposed that, if R0 is less than 1, the disease will die out in a population, because on average an infectious person will transmit to fewer than one other susceptible person. On the other hand, if R0 is greater than 1, the disease will spread.
When public health agencies are figuring out how to deal with an outbreak, they are trying to bring R0 down to less than 1. This is tough for diseases that have a high R0.
When SARS2 arrived, it was assumed the R0 was similar to the previous epidemics. Initially SARS2, the novel coronovirus, was spreading within a range of 2.2 to 2.7 then it shot up to 4.7 – 6.6
This places it in the realm of Smallpox which has an R0 of 5–7.
You can read more on How Scientists Quantify the Intensity of an Outbreak Like COVID-19
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