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Despite China's success in controlling the COVID-19 outbreak insofar, a March 31 Science paper that analyzes the response has this intriguing (and alarming) observation

The dispersal of COVID-19 from Wuhan was rapid (Fig. 3A). A total of 262 cities reported cases within 28 days. For comparison, the 2009 influenza H1N1 pandemic took 132 days to reach the same number of cities in China (see methods in Supplementary Materials).

China was surely less developed economically a decade ago, but still the 132 vs 28 days is a large difference. That paper doesn't seem to advance any hypothesis for this difference. So, is any of it based on intrinsic differences between the two viruses, or is it all down to so social movements having changed dramatically in China? Are there any other papers (e.g. on other regions on the world) that can shed some light on this? E.g. was the spread of COVID-19 as fast in Italy as it was in China, for example, and the spread of H1N1/09 just as slow?

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The most obvious reason ( apart from the fact that 5M workers who lived in Wuhan were allowed to leave and return to their home cities ) is that Covid-19 is most infectious in the immediate period before symptoms develop, whereas influenza is most infectious after symptoms develop. The symptomatic would know they had the infection and would start to self isolate. The asymptomatic had no idea that they were infected and had no opportunity to do so.

H1N1 was also less contagious

The H1N1 flu was also less contagious than the novel coronavirus. The basic reproduction number, also called the R-nought value, is the expected number of individuals who can catch the virus from a single infected person. For the 2009 H1N1 virus, the mean R-nought value was 1.46, according to a review published in the journal BMC Infectious Diseases. For the novel coronavirus, the R-nought value is estimated to be between 2 and 2.5, at the moment.

This is the nightmare scenario for Covid-19 that is playing out.

https://www.livescience.com/covid-19-pandemic-vs-swine-flu.html

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