Thread by @drdagly

Lots of questions about dosing schedules right now as Alberta opens up second shots. I’m pretty stoked about this btw.

First, these schedules are really just how the research protocols are put together when doing the original trials to test a new vaccines. For the Adenovirus vaccines they mostly followed protocols from other AV studies, except they needed to abbreviate them cuz time was short.

That’s why when the dust settled they did follow up research to see if longer dosing intervals evoke better response amplification and hence better efficacy. They compared 6 and 12 weeks. 12 weeks was better, but 6 was still very good.

As mRNA vaccines were new to human trials they again picked arbitrary intervals based on immunological plausibility. These intervals panned out very well. In all of these original studies, variants were just starting to emerge.

AZ efficacy numbers actually looked lower than Pfizer, as B117 was circulating at that time. Still it kicked butt. Now there’s another issue. B.1.617.2. It wasn’t around when these dosing studies were done. It has some vaccine resistance. Not a problem if you are double dosed.

But not up to WHO standard with a single dose. So now the crux of this argument is what is the minimum time we can go between two shots and still have robust immunity. Irony right there I tell you.

There is a time component here too. As we are opening up quickly 😬 a partially vaccinated population will select out B1617.2 as the dominant strain just as it is happening in England. That comes with many of the problems we’ve seen before.

So the best bet now is the fastest road to double shots. Pfizer’s original studies were 3 week dosing intervals, and AZ was authorized for 4, so it’s reasonable to space all three available vaccines out by a month given the situation. So ...

What do I think?
1. If you’ve had Pfizer or Modena, get a booster if you had your first shot a month ago or more. You could push it to 3 weeks.
2. If you can get your AZ booster a month after your first shot, do it. Also blood clots are even more rare with a second dose.

3. If you’ve had AZ and you can’t get a second dose in a timely manner, go for a Pfizer or Moderna booster. There is good real world evidence that this is safe and effective.

If we get 70-80% of our population double dosed we will have this thing in the bag and reduce the risk of future variants.

Again Alberta. Thanks for looking after your vulnerable neighbours who can’t get the shot. 🙏🙏🙏

Almost forgot, you’ll need 2 weeks after you’re second shot for full immunity. NO CHEATING!! 🚨🚨🚨