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expert reaction to new estimates of infection rate of novel coronavirus

A team at Imperial College London have revised their estimate of the infection rate of the Wuhan coronavirus. 

 

Dr Mike Turner, Director of Science, The Wellcome Trust, said:

“It is quite easy to get fixed on a particular number but such predicted numbers will vary considerably at this early stage in an epidemic. What is becoming clear from several sources though is that there is substantive human to human transmission and that there may well be a lot of people who become infected but have no symptoms or very mild symptoms so don’t need to seek medical attention. This makes it more difficult to put in place effective control measures.  A lot of people are working furiously to try and control this epidemic. We should continue to be vigilant but not alarmist.”

 

Professor Paul Hunter, The Norwich School of Medicine, University of East Anglia said:

“The reproductive ratio (R0) is an estimate of the average number of new people a person with the infection also infects. R0 is one of the fundamental parameters in mathematical epidemiology. Determining R0 can certainly help towards predicting the spread of an outbreak but there are still significant areas of uncertainty. R0 does vary depending on context and is influenced by biological and social factors such as how crowded populations are. In densely population communities R0 will be higher than is sparsely populated ones. One of the factors in the spread of the SARS epidemic was that hospitals served as important amplifiers of transmission and another was super spreaders that infected considerable number of individuals. Both these factors make determination of R0 in the community difficult.

“Notwithstanding the two papers that have presented estimates of R0 and estimated possible epidemic trajectories, I consider it too early to predict future spread with any degree of certainty. If hospitals have played a major role in the spread in the current outbreak after the initial wave of cases from the seafood market, then improved hospital access and facilities would have a big effect on subsequent transmission. Also of note, is that early cases in the current outbreak report upper respiratory tract symptoms less frequently than did SARS patients. If current patients are not reporting sore throats and runny noses, then it is possible that they are less infectious early on the course of the disease reducing community risk at a time before people are admitted to hospital.

“Whist the estimates of outbreak size in the paper by Read may prove correct they should not be seen as inevitable. The best approach we have to controlling this outbreak is early diagnosis of new cases before they become too ill with subsequent care in hospitals able to provide good quality nursing care and adequate infection control. Nor should we take this paper as an indication of what may happen in European countries.  Our experiences over the past 20 years with SARS and MERS have shown that we can manage the threat to public health in this country. But there is no room for complacency and we need to closely watch how the outbreak develops and ensure rapid diagnosis and effective management of any suspected cases that appear in the UK.”

 

Professor Neil Ferguson, Imperial College London, said:

“Self-sustaining human-to-human transmission of the novel coronavirus (2019-nCov) is the only plausible explanation of the scale of the outbreak in Wuhan. We estimate that, on average, each case infected 2.6 (uncertainty range: 1.5-3.5) other people up to 18th January 2020, based on an analysis combining our past estimates of the size of the outbreak in Wuhan with computational modelling of potential epidemic trajectories. This implies that control measures need to block well over 60% of transmission to be effective in controlling the outbreak. It is likely, based on the experience of SARS and MERS-CoV, that the number of secondary cases caused by a case of 2019-nCoV is highly variable – with many cases causing no secondary infections, and a few causing many. Whether transmission is continuing at the same rate currently depends on the effectiveness of current control measures implemented in China and the extent to which the populations of affected areas have adopted risk-reducing behaviours. In the absence of antiviral drugs or vaccines, control relies upon the prompt detection and isolation of symptomatic cases. It is unclear at the current time whether this outbreak can be contained within China; uncertainties include the severity spectrum of the disease caused by this virus and whether cases with relatively mild symptoms are able to transmit the virus efficiently. Identification and testing of potential cases need to be as extensive as is permitted by healthcare and diagnostic testing capacity – including the identification, testing and isolation of suspected cases with only mild to moderate disease (e.g. influenza-like illness), when logistically feasible.”

 

Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“If the numbers in the Read paper are correct then already the size of the outbreak exceeds the largest and most deadly novel Coronavirus outbreak of SARS. But these are still early days and as the authors acknowledge, the robustness of the data is very much dependent on the accuracy of the models and the assumptions made on likely level of infection and how the virus might be behaving.

What I think these data to tell us that we need to gain a better understanding what’s going on in China. In particular how the virus is being spread, whether individuals with mild or no symptoms can transmit the virus, and of course where the virus came from in the first place. I suspect that this type of real-life information will be more valuable.”*

 

Professor Mark Harris, School of Molecular and Cellular Biology, University of Leeds, said:

“Its true that the numbers in the Jonathan Read paper look scary, however the authors do make some significant assumptions which they built into their mathematical model.  So I think the numbers need to be considered in that context.

“One positive spin is that if we are only aware of 5% of the total cases, the implication is that 95% of cases have only resulted in either mild symptoms such that the infected people did not consider it serious enough to seek medical help, or indeed the virus may be causing an inapparent infection.  This would significantly reduce the apparent mortality and morbidity rates.   If at current rates 41/1400 people have died, taking into account that 1400 is only 5% of the total that means 0.1% mortality, less than flu.   Perhaps this analysis might be important when considering the implications of the paper.”

 

Notes to Editors

 

All our previous output on this subject can be seen at this weblink: http://www.sciencemediacentre.org/tag/wuhan-coronavirus/

 

Declared interests

None received. 

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