New research tests the new coronavirus ‘ basic reproduction number (R0), that is, the number that shows how transmissible a virus is, and considers it far higher than current estimates.
Scientists have been dealing with the highly contagious new coronavirus, now called 2019-nCoV, or Covid-19, since its outbreak in December 2019.
“Where did the virus come from?,” “How was that spread to humans?,” and “How long survives the virus on surfaces?” These are just a few of the questions to be answered by researchers.
Now, a study of existing studies aims to address another question critical to managing the epidemic: How quickly does it spread?
The issue is of utmost importance, especially in the light of the most recent toll: as of February 11, 2020, there have been 42,708 confirmed cases and 1,017 deaths in China.
A team of researchers set out to investigate several scientific studies of the new virus to find the answer, and published the results in the Journal of Travel Medicine.
Higher estimates than WHO predict
As Rocklöv and team explain in their paper, simple R0 defines the average number of new infections that can be produced by an infectious individual in a population not previously exposed to the virus.
An R0 greater than one suggests that the number of people infected is likely to increase, while an R0 of less than one suggests that the viral transmission “is likely to die out.”
“The basic reproduction number is a central concept in the epidemiology of infectious diseases, indicating the risk of an infectious agent with respect to epidemic spread,” the authors of the paper write.
The researchers have therefore accessed many qualifying studies dealing with the basic RO from the repositories of PubMed, bioRxiv, and Google Scholar.
Between 1 January 2020 and 7 February 2020, the studies appeared and Rocklöv and team agreed on a final number of 12 studies whose standard was good enough to be included in the study.
The studies they chose in China and overseas projected baseline R0 for Covid-19. These estimates ranged from 1.4 to 6.49 and averaged 3.28 and a 2.79.
Both of these figures are considerably higher than the numbers proposed by the WHO— which were 1.4–2.5.
The authors show that the initial studies reported lower values of R0 and then spiked back to the initial estimates. In these differences the estimation methods used by the studies played a role, the researchers note.
“The studies using stochastic and statistical methods for deriving R0 provide reasonably comparable estimates. The studies using mathematical methods, however, produce estimates that are, on average, greater.”
Coronavirus spreads faster than SARS
“Our analysis shows at least as transmissible as the SARS virus is the coronavirus. And that says a lot about the situation’s severity,” Rocklöv remarks.
“When looking at the development of the corona epidemic, reality seems to correspond well to or even exceed the highest epidemic growth in our calculations. Despite all intervention and control activities, the coronavirus has already spread to a significantly higher extent than SARS did.”– Joacim Rocklöv
Nevertheless, in their paper the scientists concede that the current estimates for the basic RO could be distorted due to the short onset of the virus and insufficient data.
“Nonetheless, as more data is collected, estimation error can be expected to decrease, and a clearer picture will develop,” writes the authors, concluding, “Based on these factors, R0 is predicted to be around 2–3 for 2019-nCoV, which is roughly consistent with the WHO estimate.”