The basic reproduction number, or R, of coronavirus transmission may have been underestimated in the early stages of the Covid-19 pandemic, according to scientists.
Researchers based in Poland used a type of epidemiological model known as SEIR (Susceptible Exposed Infectious Removed) to calculate the value of R by looking at data from eight countries, including the UK.
Their results, published in the journal Royal Society Open Science, suggest an R value of between 4.7-11.4 at the start of the pandemic, much higher than the 2-4 previously estimated.
R is the number of people that one infected person, on average, will pass on a virus to.
For example, if a disease has an R of four, a person who has the disease will transmit it to an average of four other people.
A preliminary estimate published by the World Health Organisation (WHO) suggested R was between two and 2.5 in early March.
Meanwhile, scientists in the UK estimated R to be between two and three at that time – higher than the value for seasonal flu, but lower than for measles.
But researchers led by Marek Kochanczyk, of the Polish Academy of Sciences, suggest a small group of super and hyper spreaders initiated the exponential growth phase of Covid-19, decreasing the doubling time of the disease and, consequently, driving up the R estimate.
The authors wrote: “The simulations revealed two-phase dynamics, in which an initial phase of relatively slow epidemic progression diverts to a faster phase upon appearance of infectious super-spreaders.”
The estimates of R are based on models of the progression of the Covid-19 disease in China, Italy, Spain, France, the UK, Germany, Switzerland and the US.
The researchers said that once these regions implemented measures to slow down the spread of the virus – such as lockdowns, quarantines and social distancing – R was “reduced more than fivefold, which brought it to the values somewhat smaller than one”.
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