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expert reaction to study looking at the incubation period of COVID-19

Research, published in the Annals of Internal Medicine, reports that people infected with coronavirus may be symptom-free for 5 days.


Prof Peter Openshaw, Professor of Experimental Medicine, Imperial College London, said:

“The analysis shows that one case in 100 will fall outside the current 14 day incubation period, which seems to encompass the vast majority of infections.  Given that no isolation advice will be adhered to perfectly, there seems no justification for changing the recommendation that 14 days of isolation is sufficient.  It is difficult to explain the variations in incubation period, which might depend on the level of exposure and the resistance of the mucosa to infection.  More studies are needed to determine the causes of this variability.”


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

“This study confirms that for the vast majority of cases, the incubation period for the novel coronavirus will be up to 14 days, with most people showing evidence of infection within 5 days or so.  Whilst the study suggests that in some people the incubation period might be longer, we have to acknowledge that the models they use to estimate incubation period make key assumptions, and perhaps the assumption most likely to impact on their data is that a person became infected as soon as they came into contact with the virus.  This might not be true – the real infection timepoint might be much later, yet assuming the infection occurred at an earlier date will make the incubation period appear longer.

“I think it is really important when dealing with this outbreak that we fully understand the limitations of studies and their findings and also base any intervention or policy on norms, not extremes.  As it stands there is little evidence to suggest that a quarantine or self-isolation period of 14 days is not suitable.  Also, there is little if any evidence that people can routinely transmit virus during the asymptomatic period.”


‘The incubation period of coronavirus disease 2019 (COVID-19) from publicly reported confirmed cases: estimation and application’ by Stephen A. Lauer et al. was published in the Annals of Internal Medicine at 21:00 UK time on Monday 9 March 2020.

DOI: 10.1101/2020.02.02.20020016


All our previous output on this subject can be seen at this weblink:

The SMC also produced a Factsheet on COVID-19 which is available here:


Declared interests

None received.

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