The effect of social distancing on COVID-19 spread?

[oxmixmudd]

I was looking over the data, specifically the slow ramp down in US data. What you will notice is that it is bumpy - up/down/up/down. What you might not notice is that the period is 7 days, and further, that the number of cases always hits a low on a Wednesday/Thursday, then grows until a Sunday/Monday, and then falls again until the next Wednesday/Thursday. (Interestingly, between yesterday and today, the worldometers switched to a 7 day average from a 3 day average overlay of the daily data which to a certain extent makes the periodicity a little less obvious in the continuous overlay)
.

US_daily_active_cases_05062020.jpg

Likewise, this same periodicity can be seen in the graph of daily deaths. Only it is delayed approximately 11 to 12 days.

US_daily_deaths_05062020.jpg

the curve tends to grow for 4 days and decay for 3. One possibility is that this periodicity is driven by the work week interaction of essential workers, people out shopping etc. Average incubation is 5.2 days, but the delays from first symptom to test to test result can be another 3 to 7 days. So it it very hard to say for sure what sort of weekly interaction is showing up here, but a fixed period of 7 days almost certainly points to some sort of correlation with the work week itself, which would tend to imply periods where we are out and about (work days?) produce more spread than periods where we tend to be at home with just our local family (weekends?)

I tend to think we are seeing the effect of social distancing on a weekly basis where periods of high interaction clearly show up as weekly peaks in the number of new cases per day, but there are a lot of variable that I don't have statistics for (when do people shop the most, what % are essential workers going to work 5 days a week vs 7 days a week (e.g. hospital workers) etc. What are the average delays between symptoms and testing/testing and test result. I can find ballpark guesses (like test result take from 2 days to a week) but that doesn't really help much.

What does seem to line up with the statistics is the delay between active case peak and death peak of 11 days or so. worldometers lists 14 days as average from first symptom to death giving an average 2 to 3 days delay for diagnosis -which seems in the right ball park.

If this periodicity represents the result of weekly increases in interaction under shelter in place just due to essential shopping and essential workers interacting, it does not bode well for relaxing those restrictions. That will increase interactions, and as it is we are barely on a ramp down. Increase those interactions by a factor of even just 2 by opening up and that downward slope will shift to an upward one.


I welcome any comments or alternate explanations for the 7 day cycle and active/death peaks.

[Ronson]

Not as much testing done on weekends, perhaps.

[oxmixmudd]

Not as much testing done on weekends, perhaps.

I believe that would show up as a more direct correlation of the growth period with with Mon - Friday. Growth is delayed about 4 days and the growth period is Thursday -> Sunday/Monday.

[Sparko]

most likely has to do with how and when the data is reported and entered in my opinion.

[oxmixmudd]

most likely has to do with how and when the data is reported and entered in my opinion.

The data is gathered across the day and then updated daily at the JHU site. Worldometers appears to update in real time but that depends somewhat on the source. Do you have an idea for how one could end up with a weekly periodicity associated with daily data gathering and reporting across the whole of the US other than it reflecting an actual weekly pattern of disease diagnosis/occurrence of death? This has been the pattern for 4 weeks.

[shunyadragon]

Interesting conclusions. It is possible our weakness of social distancing may contribute to the pattern you see.

I noticed tis cyclic pattern before, but just averaged the figures and trends to arrive at my conclusions for the peak being between last half of April and first half of May centered on May 1. I will have to follow this more closely.

Some other countries with more homogenous populations, and isolated like New Zealand and Australia with less variables have a more distinctive uniform bell curve.

Thank you for the insight!

[mikewhitney]

I was looking over the data, specifically the slow ramp down in US data. What you will notice is that it is bumpy - up/down/up/down. What you might not notice is that the period is 7 days, and further, that the number of cases always hits a low on a Wednesday/Thursday, then grows until a Sunday/Monday, and then falls again until the next Wednesday/Thursday. (Interestingly, between yesterday and today, the worldometers switched to a 7 day average from a 3 day average overlay of the daily data which to a certain extent makes the periodicity a little less obvious in the continuous overlay)
...

Likewise, this same periodicity can be seen in the graph of daily deaths. Only it is delayed approximately 11 to 12 days.
...

the curve tends to grow for 4 days and decay for 3. One possibility is that this periodicity is driven by the work week interaction of essential workers, people out shopping etc. Average incubation is 5.2 days, but the delays from first symptom to test to test result can be another 3 to 7 days. So it it very hard to say for sure what sort of weekly interaction is showing up here, but a fixed period of 7 days almost certainly points to some sort of correlation with the work week itself, which would tend to imply periods where we are out and about (work days?) produce more spread than periods where we tend to be at home with just our local family (weekends?)

I tend to think we are seeing the effect of social distancing on a weekly basis where periods of high interaction clearly show up as weekly peaks in the number of new cases per day, but there are a lot of variable that I don't have statistics for (when do people shop the most, what % are essential workers going to work 5 days a week vs 7 days a week (e.g. hospital workers) etc. What are the average delays between symptoms and testing/testing and test result. I can find ballpark guesses (like test result take from 2 days to a week) but that doesn't really help much.

What does seem to line up with the statistics is the delay between active case peak and death peak of 11 days or so. worldometers lists 14 days as average from first symptom to death giving an average 2 to 3 days delay for diagnosis -which seems in the right ball park.

If this periodicity represents the result of weekly increases in interaction under shelter in place just due to essential shopping and essential workers interacting, it does not bode well for relaxing those restrictions. That will increase interactions, and as it is we are barely on a ramp down. Increase those interactions by a factor of even just 2 by opening up and that downward slope will shift to an upward one.


I welcome any comments or alternate explanations for the 7 day cycle and active/death peaks.

Indeed, there will be lots of people wanting to make a case to suppress us longer and to explain subsequent "outbreaks." There will be lots of cycles of hope and despair that will be promoted.

There are probably some real situations that could cause such fluctuations of this type of data, even when not part of a virus scare. If this depends on people getting tests done, it depends on where testing is done and when it is available. A more typical cycle to note is that people have often waited until the weekdays to go to the emergency room, even if sick through the whole weekend. We can only speculate why the data has funny patterns, so it is risky to ascribe it to disruptions of social distancing.

[shunyadragon]

To add we are a very mobile social diverse society dealing with a coronavirus where as much as 80%+ infected are asymptomatic or with very mild symptoms.

[shunyadragon]

Indeed, there will be lots of people wanting to make a case to suppress us longer and to explain subsequent "outbreaks." There will be lots of cycles of hope and despair that will be promoted.

There are probably some real situations that could cause such fluctuations of this type of data, even when not part of a virus scare. If this depends on people getting tests done, it depends on where testing is done and when it is available. A more typical cycle to note is that people have often waited until the weekdays to go to the emergency room, even if sick through the whole weekend. We can only speculate why the data has funny patterns, so it is risky to ascribe it to disruptions of social distancing.

First, it is very foolish to call it a 'virus scare.' Second it is very well documented that the spread of this coronavirus is directly related groups and crowds, including meetings and parties where much of the early spread of the infection. The other assumptions above are heavy speculation.

[Starlight]

Not as much testing done on weekends, perhaps.

In my country it's been observed that fewer people go in to be tested in weekends.

Either people wrongly assume testing facilities won't be open at weekends, or they have better uses for their leisure time and would prefer to spend work hours getting tested.

[mikewhitney]

First, it is very foolish to call it a 'virus scare.' Second it is very well documented that the spread of this coronavirus is directly related groups and crowds, including meetings and parties where much of the early spread of the infection. The other assumptions above are heavy speculation.

If it is not a virus scare, is it to be called a virus pleasure instead? I'm not sure your point here.

Next time you should gather some facts before you post. Anyhow, the point about the emergeny room behavior was reported to me by an emergency room worker.

[shunyadragon]

If it is not a virus scare, is it to be called a virus pleasure instead? I'm not sure your point here.

Next time you should gather some facts before you post. Anyhow, the point about the emergeny room behavior was reported to me by an emergency room worker.

You are the one that used 'virus scare' in your post. Please clarify.

[Sparko]

The data is gathered across the day and then updated daily at the JHU site. Worldometers appears to update in real time but that depends somewhat on the source. Do you have an idea for how one could end up with a weekly periodicity associated with daily data gathering and reporting across the whole of the US other than it reflecting an actual weekly pattern of disease diagnosis/occurrence of death? This has been the pattern for 4 weeks.

I remember Dr. Birx mentioning at one of the press conferences, a "monday spike" of new cases because of lower reporting over the weekend (which I assume they catch up on Monday). Which I would think would mean it would then get lower again tuesday-wednesday.

Also, I don't think the periodicity would be because of people being more active on certain days, because the incubation period is widely variable. For that periodicity to show up the incubation period to testing positive would have to be very consistent. It could also reflect testing on specific days. If they test more people on certain days than others, then the results will reflect that.

[oxmixmudd]

I remember Dr. Birx mentioning at one of the press conferences, a "monday spike" of new cases because of lower reporting over the weekend (which I assume they catch up on Monday). Which I would think would mean it would then get lower again tuesday-wednesday.

Also, I don't think the periodicity would be because of people being more active on certain days, because the incubation period is widely variable. For that periodicity to show up the incubation period to testing positive would have to be very consistent. It could also reflect testing on specific days. If they test more people on certain days than others, then the results will reflect that.

It's not a spike on monday but steady growth from thursday to sunday/monday, but what birx mentions could realistically be a component of the trend.

I would say you might have a point in the second paragraph if the distribution of incubation is not gaussian or skewed gaussian ( IOW if it doesnt have a strong peak around the mean). However, what I've seen does peak around the mean with the likelihood of an outlier decreasing substantially as you move away from that 5 day average, which means we'd still see activity based correlations as most would show first symptoms 4 to 5 days from infection.

[Bill the Cat]

My oldest is actually doing the COVID tests for my region. Her take is that they don't get many tests delivered to them on Monday because the delivery companies don't deliver to them on Sunday. They test all day, enter their findings later that evening and publish them the next day. So if testing doesn't pick up until Tuesday, the findings are not made available until Wed. Since no testing is done on the weekends at her company, there will be no data to report for the first few days of the week.