London School of Hygiene & Tropical Medicine

The team used a mathematical model, incorporating multiple datasets to make the analysis as reliable as possible, to estimate how the basic reproduction number (R0) of 2019-nCoV changed in the early stages of the outbreak.

This number is the average number of people who will catch the disease from a single infected person, in a population that’s never seen the disease before.

They found that the 2019-nCoV R0 fluctuated between 1.5-4 before travel restrictions were introduced on 23 January, with evidence for a reproduction number of over two in December/January, suggesting an early surge in human-to-human transmission during this period.

However, the team found that the reproduction number declined after this period of high transmission, which may explain why cases in Wuhan have levelled off in recent days, and fewer travellers from Wuhan were becoming ill prior to the travel restrictions being introduced.

Adam Kucharski, Associate Professor at LSHTM and a member of the modelling team, said “It’s important we further our understanding of how this new virus transmits between humans so we can estimate what might happen as the outbreak continues. Establishing its reproductive number makes it possible to work out how easily the infection is spread, and what might be required to control it.

“Our model suggests that exported cases linked to Wuhan will continue to be observed in the coming days, but gradually decline as the effect of the travel restrictions begins to be seen. An even stronger indication of how transmissible this virus is will be possible when children return to school in Wuhan – settings which provide optimum conditions for infectious diseases to spread.”

The group previously used a similar analysis to understand the dynamics of Ebola in Liberia. In the new analysis they assumed that the chance of cases being exported from Wuhan to other countries depended on the number of cases in Wuhan, the number of outbound travellers (accounting for travel restrictions after 23rd January), and the relative connectivity of different countries.

They considered the 30 countries outside China most at risk of exported cases in the analysis, and accounted for delays in symptom onset and reported reductions from control measures.

Adam Kucharski said: “Although it’s useful to get a better idea of transmission in Wuhan, we still don’t know how easily the virus could transmit between humans outside of China. This is crucial information that will help us assess the risk of outbreaks in other areas.”

This analysis has not been peer reviewed. The team say there are limitations to their work, including current uncertainty about the precise characteristics of the infection and how many cases have become ill in Wuhan in recent days.

• Preliminary analysis of transmission and control of nCoV in Wuhan
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