I am puzzled at how mild interventions don’t show a much bigger decrease.
In Ottawa, where I live, we have social distancing and have shutdown non-essential places of business. If you work in a closed business, you have probably reduced your person-to-person contacts from (guessing) 300 per week to maybe 50 -- those 50 being people at grocery stores, etc. Moreover, the intensity of those instances of contact has dropped. You may have played poker with 10 people, mutually touching cards and chips and sitting together for hours. Now, you stand within 2m of a store cashier for a couple of minutes.
Just this 83% drop—which I think is conservative—should push R down from 3 (without intervention) to 0.5.
Add in hygiene improvements and more aggressive quarantining of those with symptoms, and R should drop even farther below 0.5.
If my numbers and logic are reasonable, the reason we haven’t seen a lot of dropoff yet must be because of legacy cases (from before intervention) still coming in and obscuring the current trajectory. (We’ve only had serious social distancing for 12 days or so.)
Unless there’s there something wrong with my calculations or logic. Are my estimates of contact frequency (300, 50) badly off?
You can reduce your contact, but what about your contacts contacts?
How many people is the person serving in the grocery store coming into contact with?
How strict are they all with their precautions?
What about other members of the same household and all their contacts?
The recommended distance between people may not be sufficient to prevent transmission.
It’s easy to break the distance rule (might just be a second or two even if being v. careful).
Fomite transmission (inanimate carrier of infectious diseases)
Pre-(noticed) symptomatic transmissions. What if someone has a fever during the night, how many people would notice it/associate it with COVID? (It always amazes me the denial some people can have about their symptoms.)
QUESTION - has anyone come across data about duration of a COVID-fever? (although there’s a massive potential for variability between individuals so not sure the data would actually be useful/representative/meaningful but it’d be good to have whatever information is out there...)
All these points make sense. But aren’t they also (with the exception of the one about members of the same household) subject to the logic that they reduce roughly proportionally to reduced contacts? For instance, even in the unlikely case my contacts’ contacts are not reducing, I am still reducing contacts with my contacts’ contacts by reducing contacts with my contacts.
I am puzzled at how mild interventions don’t show a much bigger decrease.
In Ottawa, where I live, we have social distancing and have shutdown non-essential places of business. If you work in a closed business, you have probably reduced your person-to-person contacts from (guessing) 300 per week to maybe 50 -- those 50 being people at grocery stores, etc. Moreover, the intensity of those instances of contact has dropped. You may have played poker with 10 people, mutually touching cards and chips and sitting together for hours. Now, you stand within 2m of a store cashier for a couple of minutes.
Just this 83% drop—which I think is conservative—should push R down from 3 (without intervention) to 0.5.
Add in hygiene improvements and more aggressive quarantining of those with symptoms, and R should drop even farther below 0.5.
If my numbers and logic are reasonable, the reason we haven’t seen a lot of dropoff yet must be because of legacy cases (from before intervention) still coming in and obscuring the current trajectory. (We’ve only had serious social distancing for 12 days or so.)
Unless there’s there something wrong with my calculations or logic. Are my estimates of contact frequency (300, 50) badly off?
What am I missing?
A couple of additional points to leggi:
Elizabeth calculates roughly 25% of people are in essential roles. These people are less able to reduce numbers of contacts.
At least initially many people don’t take social distancing seriously so the effects are likely to ramp up over time.
In that case it makes sense that initially doubling times increase over 5 and over time they keep increasing.
In China the distance was enforced and Koreans took it seriously right away so it didn’t take long for their doubling times to increase.
Some first thoughts:
It only takes one person to infect you.
You can reduce your contact, but what about your contacts contacts?
How many people is the person serving in the grocery store coming into contact with?
How strict are they all with their precautions?
What about other members of the same household and all their contacts?
The recommended distance between people may not be sufficient to prevent transmission.
It’s easy to break the distance rule (might just be a second or two even if being v. careful).
Fomite transmission (inanimate carrier of infectious diseases)
Pre-(noticed) symptomatic transmissions. What if someone has a fever during the night, how many people would notice it/associate it with COVID? (It always amazes me the denial some people can have about their symptoms.)
QUESTION - has anyone come across data about duration of a COVID-fever? (although there’s a massive potential for variability between individuals so not sure the data would actually be useful/representative/meaningful but it’d be good to have whatever information is out there...)
All these points make sense. But aren’t they also (with the exception of the one about members of the same household) subject to the logic that they reduce roughly proportionally to reduced contacts? For instance, even in the unlikely case my contacts’ contacts are not reducing, I am still reducing contacts with my contacts’ contacts by reducing contacts with my contacts.