Moving out of lockdown - what happens?

Moving out of lockdown  - what happens? 

What does a controlled epidemic look like?

Here is our Pandemicia graph of new infections in two countries that have managed to suppress their COVID-19 outbreaks, showing what a typical controlled coronavirus epidemic looks like. The patterns are quite similar, despite taking place in very different countries using different strategies.

New confirmed cases in South Korea and Australia, starting from N=100

They both show about 9-10 days of rapid expansion to the maximum ‘inflection point’, another 9 days while it rounded off, and another 9-10 days when it fell back down to a ‘background level’ of less than 100 cases a day. Korea now has about 10 cases a day, Australia about 25.

Here however is the pattern in the USA.

New confirmed cases USA
Source: Johns Hopkins

In the USA, confirmed cases went up for much longer, around 25 days, before the epidemic was arrested by lockdown. If the same scale is maintained, it will spend 25 days rounding off (another week to go) and then 25 more days before it comes down to a manageable level – a month from now. 

Unfortunately, there also remains a data argument that the USA epidemic has not yet been arrested, which we will present separately.  

So what happens if the lockdown is now relaxed, as promised by President Trump and some State governors?

Superspreader clusters

The problem with coronavirus epidemics and why they are so hard to stop, is that they start mostly from ‘superspreader’ clusters or bubbles. We now have many well-documented examples of these around the world, not just from SARS-CoV-2 but from predecessor coronavirus outbreaks.

For a short period of time, usually at most a couple of days, a superspreader spreads the virus to anyone within range. In a couple of hours 35 people can be infected at a gathering; in a couple of days in a crowded environment, many more.

These superspreaders cause the early part of an epidemic to ramp up very quickly. All of a sudden there are cases everywhere, with potentially thousands of contacts in a week, particularly if a second superspreader takes over from the first.

Suppose for example, two superspreaders spread to 80 people in 6 days. After that, cases go up by 25 per cent a day, which has been typical for COVID-19. In another 54 days, the number of cases will be about 14 million from the original case, with deaths over 100,000.  

 It is this superspreader bubble scenario that has discouraged Korea and Australia from relaxing their lockdowns, even though their daily cases are now so low.

What about if you are still near the top, like the USA? 

What happens if you open the gates for an epidemic that is still in high flight, but has been slowed, as in the USA?

Presumably it just starts expanding again from where it was before. After an appropriate interval it will be expanding at 25% a day again. From there it rages until the ‘herd immunity point’ is reached and the disease runs out of people to infect, after which it dies out of its own accord and becomes part of the background or seasonal disease burden forever. This seasonal burden is not insignificant - influenza already kills tens of thousands of people a year.

How long is that appropriate interval? That depends on what you do. It is possible you might still be able to suppress the disease, while keeping your economy running. 

Nobody has really tried intermediate alternatives to lockdown for very long. For example, if you continue to prohibit large gatherings, you might stop the superspreaders and keep a cap on infections. If you can block superspreading, you have a fair chance of hunting down any smaller infections before they get out of hand.

The problem is – can you really stop all parties and gatherings when the population is not in lockdown? And what happens when you have hundreds or thousands of superspreaders going at once, which you may well have if you relax all prohibitions in a large country with a wide base of infection like the USA? The prospects are not pretty.

<Return to Index>