Thread. Will explain from first principles how China put itself in a good position to come out of lockdown, why it will be harder for the West and the broad principle it needs to adopt to make a smooth transition to normality feasible 1/15

The first principle is simple. You can come out of lockdown when (almost all of) the people who are infectious are separated from (almost all of) those who are susceptible, i.e. to those who have not been infected. 2/15

China started to return step by step to normal life about the same time I returned there from a trip from Europe, on February 19th. At this point there were about 350 cases in Shanghai, that were all in hospital or recovered. 3/15

Anyone in the same compound as a case or a known contact was self-quarantining and there were still ongoing pockets of transmission, most especially in Wuhan and the rest of Hubei province, but these areas were cut off. Thus, susceptible and infected were mostly separated. 4/15

And to the extent that that they were not segregated, some version of the lockdown continued, locally. Recently, this has extended to the external borders. People who enter China have to do increasingly rigorously enforced quarantines. 5/15

In addition, there remains a considerable, rather low-tech surveillance apparatus in place. Mainly, everyone gets their temperature taken regularly, e.g every morning at work. And obviously the higher tech fever clinics are still set up ready to examine any suspicious cases. 6/15

Restrictions have lifted progressively. Now restaurants are open but not cinemas or live music. It still takes a bit of bravery to travel, mainly due to the possibility of ending up stranded far away from home, although its increasingly possible. So far, its gone smoothly. 7/15

If the current measures employed in the west were maintained, it would take months and months or longer to achieve a similar segregation of susceptible and infected This is clearly not feasible on economic and other grounds. 8/15

So broadly, there are two possibilities, (1) come out of lockdown and accept an increase in transmission or (2) work continuously towards a better segregation of infected and susceptible individuals that goes along with an easing of some restrictions. 9/15

I think that (1) would prove to be protractedly painful and ultimately fail. the gains from the lockdown would be undone quickly and it will become increasing hard to control infection or the population. 10/15

(2) can be achieved, for example if coming out of the lockdown went hand in hand with establishing health status. For example, every individual in a household might have to submit their temperature for 5 days before being allowed to return to work 11/14.

furthermore, as discussed in this thread, https://twitter.com/DanielFalush/status/1245950157021036546 voluntary centralized quarantining of infected individuals is a no-brainer from a health perspective, especially the families of those quarantined. It is also unexpectedly palatable in practice. 12/14.

Also, well discussed measure include contract tracing, becomes progressively more feasible as case numbers reduce and antibody tests which identify recovered, non infectious individuals. Also see the health code app in China and also those good old temperature checks. 13/14.

The golden rule in the West should be that in any given time period, the effective segregation of infected and infectious individuals needs be maintained or increased. As long as this is happening, the population is moving in the right direction, out of COVID-19 misery 14/14.