In a review of previous studies, a team of researchers from Sweden, Germany and China found the average reproduction number (R0) for the COVID-19 coronavirus to be 3.28, which exceeds World Health Organization (WHO) estimates of 1.4 to 2.5.

R0 is an indication of the transmissibility of a virus, representing the average number of new infections generated by an infectious person in a totally naïve population.

For R0 greater than one the number infected is likely to increase, and for R0 less than one transmission is likely to die out.

The basic reproduction number is a central concept in infectious disease epidemiology, indicating the risk of an infectious agent with respect to epidemic spread.

The WHO estimates that the COVID-19 coronavirus has an R0 of between 1.4 and 2.5.

“Our review shows that the coronavirus is at least as transmissible as the SARS virus,” said Professor Joacim Rocklöv, a researcher at Umeå University, Sweden.

“And that says a great deal about the seriousness of the situation.”

Professor Rocklöv and colleagues identified 12 recent studies which estimated the basic reproductive number for COVID-19 from China and overseas.

“The studies consisted of estimations of the growth rate based upon the cases observed in the Chinese population, and based upon statistical and mathematical methods,” they said.

“The earliest studies of the coronavirus indicated a relatively low transmissibility.”

“Thereafter, the transmissibility rose rapidly to stabilize between 2-3 in the most recent studies.”

The reproduction number in the studies summed up to a mean of 3.28, and a median of 2.79, which is significantly higher than WHO’s estimate of 1.4-2.5.

“When looking at the development of the COVID-19 epidemic, reality seems to correspond well to or even exceed the highest epidemic growth in our calculations,” Professor Rocklöv said.

“Despite all intervention and control activities, the coronavirus has already spread to a significantly higher extent than SARS did.”

The review paper was published in the Journal of Travel Medicine.

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Ying Liu et al. The reproductive number of COVID-19 is higher compared to SARS coronavirus. Journal of Travel Medicine, published online February 13, 2020; doi: 10.1093/jtm/taaa021