The coming vaccine wall in Ontario

First doses first was the right move, but a bill is coming due

Welcome to Plugging the Gap (my email newsletter about Covid-19 and its economics). In case you don’t know me, I’m an economist and professor at the University of Toronto. I have written lots of books including, most recently, on Covid-19. You can follow me on Twitter (@joshgans) or subscribe to this email newsletter here. (I am also part of the CDL Rapid Screening Consortium. The views expressed here are my own and should not be taken as representing organisations I work for.)


Most Covid vaccines require two shots — a second about a month after the first. I have written about this before. The immune system is complex so it needs work to provide full protection. But there is a trade-off. The first dose can provide a lot of protection. When vaccine supply is short and prevalence is high it makes sense to prioritise the first dose and lengthen the time for the second. This hasn’t been done in the US but they have enough supply. But it has been done in Canada; specifically, Ontario.

Here is what that looks like in Toronto:

You can see when we switched to first doses first; in late February. At that time, we moved from three to four weeks between doses to 16 weeks. In March, there was an increase in supply and a little more in April. But not a huge surge. Ontario is expected to get 400,000 doses per week of Pfizer through the end of May and maybe another 1,000,000 in total of Moderna in April. That is about current rates which means we will be flat through June.

I was initially sceptical about first doses first. One of the reasons is that I worried about whether the supply benefits were there. We can see this worry in the above graph. 16 weeks from mid-March is the beginning of July. At that point, everyone who was vaccinated in mid-March will need a second dose. But where will that come from. If supply rates hold steady, that will come from first doses and, if you carry that through, that means that virtually no first doses will be given between July and October. Suffice it to say: holy crap! This means that we will not have prepared for the fall when cases are predicted to surge again based on current vaccination rates which, by my maths here, can’t actually happen. So it is worse, really worse.

What this means is that to maintain current vaccination rates in Canada, we need to double dose supply by July. With the US reaching some saturation maybe that will happen. But there are headwinds.

Here is one. I was staring at this table from Christopher Murray:

The vaccines are all great in preventing hospitalisations and fatalities. But there are great differences in preventing transmissions, especially for the new variants. That is going to matter for public health. When vaccines are in short supply we really need to prevent transmission. AstraZeneca has the highest potential supply but ranks down on dealing with that. We have those variants in Ontario. It is a big problem.

First doses first was the right call but it has costs and the bill will be coming due:

  1. We need to increase supply to maintain vaccination rates. Otherwise, that mitigation grinds to a halt just as it is needed to prevent the pandemic from resurging.

  2. We don’t know what happens if we extend the length in doses from 16 weeks. I believe experts are now comfortable going from 4 to 16 weeks but we just don’t know.

  3. Pfizer believes that a third booster shot will be likely and is studying that. When that occurs is surely a function of the difference in time between the first and second shots.

We need to study this second part ASAP. Ontario has conducted an experiment. We have high prevalence. So how well are first doses working overtime? What is the drop off rate in protection? This is the information we need both now and definitely before July. At some point, we are going to have to make a hard decision on what to do about our vaccination rate. The time for preparation and information gathering is now.