Ok so then class sizes must not be as big as some people are claiming? I mean it doesn’t make sense that you have big in person classes and huge online classes but still don’t have enough teachers.
Also why do you need separate supply lists for in person and online?
As
@Disneylover99 indicates, there are a lot of forces at play here.
First, a great many more teachers than normal took early retirement this year rather than returning. In DW's school there were 2 early, and 1 scheduled retirement. Believe me, she considered it herself. A great many teachers then sought accommodations due to underlying health issues. Many were granted but many more were not (hopefully most of these are teaching online instead). So we are starting with a deficit of teachers. Now also consider that teaching is no longer the esteemed profession it once was; there are not a lot of available trained teachers waiting in the wings to step in. A great many people with teaching credentials end up in different careers because it is so difficult to break into teaching (usually takes several years of very unstable STO/LTO and partial positions before you get a full time assignment). If you have moved to another career with decent pay, would you return to teaching THIS year of all years? Probably not.
Now pressure on supply teachers. Most teachers will teach through any health issue unless they literally cannot get out of bed. But this year, if they wake up with the slightest of symptoms, they must not go to work, and must isolate until symptoms have been absent for 24 hours. That is a lot more time off work than in previous years. But who are the supply teachers. A great many of them are retired teachers who are supplementing their retirement income. They do not HAVE to work, they CHOOSE to work because it is convenient to them. They are generally a bit older than those teachers who are just reaching retirement, so are at greater risk than the main body of teachers. So I ask you, if you were in that situation, would YOU return to work if you didn't have to? Lots did not return.
ETA: This is not to imply these are the only pressures, just a couple of the ones I am aware of.
To answer another question, it was just communicated last week that supply or occasional teachers are able to teach in multiple schools, could be up to 5 (or more) per week. This was on advice of Public Health and was supported by the board and union, although I can tell you that occasional teachers are generally not very happy. But in thinking it through, I doubt this shifting about will happen much. Most schools will have no problem keeping their DOTs (designated occasional teachers) busy every day based on the conditions outlined above.
So here we are 4 weeks into the school year for some, Ottawa's largest board is just starting the 2nd full week of classes. As reported in the Citizen this weekend, nearly 20% of Ottawa schools are already reporting at least one case of COVID-19. It will be very hard to keep a lid on this, but they are doing their absolute best to keep the students safe with the resources available to them. And that is one of the messages delivered to teachers this year - it is safety first, education second.