The BC announcement providing some details of their projections has triggered a tidal wave in Canada. Ontario, Quebec, Alberta and the Government of Canada have now all issued their own reports. Looking at these projections and lots of other stats on the virus is overwhelming, and you often can’t see the big picture. What is important is to focus on what is the really new information, and what is NOT being said.
As an overall reference point, Canada, the US and the UK are largely following the Imperial College analysis. A NY Times article on why their report was so influential was in the Mar 22 blog. The Imperial College graph showing a second wave when social distancing policies are used was in the Mar 19 blog (repeated here for convenience).
https://www.nytimes.com/2020/03/17/world/europe/coronavirus-imperial-college-johnson.html
What was important about the BC projection was that it is the first time that an official has acknowledged that there will likely be a second wave in the fall. Alberta and Quebec only released projections until April 30, citing uncertainty in their model and their data to go beyond that.
The Ontario report went even further than BC and said that the effects of Covid-19 may last for 18 months to 2 years.The Government of Canada confirmed that the pandemic will continue for up to 2 years, and further that there will be a number of outbreaks after the first peak.
Here is the case from the Imperial College report that shows multiple waves over 18 months, as social distancing measures are relaxed and then reimposed when the virus starts to spread again. (This report was published March 16. It took 3 weeks for various Canadian government health authorities to release bits of information shown in this case.)
In the US, very little is being revealed about their model projections. The focus there is on whether they are reaching the peak and flattening the curve. The best way to detect that is by looking at the change in the daily number of new cases. When this number starts to fall, the curve is flattening, when there are no new cases the curve is at the peak and when new cases start to decline you are going down the other side of the curve. Here is a typical picture showing flattening the curve .
Sites that have daily updates of the daily number of new cases are:
U.S.
https://datausa.io/coronavirus
scroll to GROWTH RATE. This chart is very crowded, click on the map to select the states you want to see.
Canada
https://newsinteractives.cbc.ca/coronavirustracker/
scroll to Daily new cases. Click Canada off and click one province at a time to see the new case count in most detail.
So now here is what is not being said — Flattening the curve is NOT reducing the number of people who will get infected, it is just spreading the cases over a longer period, in an attempt to keep the hospitals from being overwhelmed. And coming down the curve on the far side, is NOT the end of the pandemic. There is likely a second wave and a third wave and so on, as shown on the Imperial College graph above.
So how does a pandemic actually end?
A pandemic occurs when someone who is infected passes on the virus to many other people. If you infect 3 people and they in turn infect 3 more people, that is a total of 3+(3 x 3)=12. If the average time to pass on the infection is 5 days, then at the end of 1 month you have passed on the virus to about 1000 people.
Each pandemic has different transmission characteristics. The numbers used in this example (3 and 5) are thought to be good estimates for Covid-19 (measured by calculating averages from many cases). As the virus spreads, more of the people you encounter have already had the virus and have recovered. They are now immune, so you now may only be infecting on average 2 people instead of 3. This is 100 people per month, down from 1000. This slows down the spread of the virus. When on average you are infecting less than 1 person, the pandemic will slow down and end.
General estimates are that 33% to 66% of the population needs to be immune before the pandemic ends.
https://www.sciencenews.org/article/covid-19-when-will-coronavirus-pandemic-social-distancing-end
A vaccine can rapidly increase the immunity in a population but this generally considered to be at least 12 months away. Social distancing restrictions can slow the spread of Covid-19, but it does NOT change immunity. The virus will continue to spread until there is enough immunity in the population to slow it down so that it is not a pandemic.
