Thread by @WheatNOil

The summary in this link is a well done explanation of their reasoning here. I can clarify more if people would like, but this is a real change in vaccine strategy if all the provinces adopt.

https://twitter.com/kellygrant1/status/1367230399139753986

Ok, here’s the deal:

When the Pfizer trials were first released, people noticed something pretty quickly. For the first couple weeks, people who got vaccine (blue) got COVID at about the same rate as placebo (red). This makes sense. It takes a bit for the vaccine to work.

But after that, the vaccine group stopped getting COVID while placebo kept going. So there was a clear benefit BEFORE the second dose (around day 21).

(I’m going to continue this later, need to stop to read Narwhal Unicorn of the Sea to 3yo. 3yo doesn’t care for my Twitter threads)

Back. As is so often the case, one book became many.

Anyways, so we have this data that suggests the vaccines start working after one dose. But it doesn’t say ‘how long’ that benefit lasts. Would the benefit drop off without a second dose? At the time, it was impossible to know.

However, we were (and are) faced with a real world dilemma. We have limited vaccine. If one dose is enough for awhile, we could save more lives by getting that first dose into twice as many people. Based on that, some places began extending the time to the 2nd dose.

So now we’re a few months in and we don’t have more clinical trial data, per say, but we do have some real world data.

What NACI commented on is that there’s some good real world evidence that immune response lasts at least 2 months after one dose.

Further, they say that your immune response doesn’t just disappear over night. If you’ve got that good of an immune response at 2 months, it’s going to last awhile longer. Your immune system doesn’t just wake up one morning & forget.

They suggested that even if you ran scenarios where your immune memory started to fade, you’d still probably sustain immunity out to 6 months or more.

So based on that, they suggested 4 months would be safe.

Now, if we had unlimited vaccine, probably we wouldn’t bother stretching things out at this point. We’d just do what happened in the trials. But we don’t have unlimited vaccines.

So we have to make a call.

If you vaccinate everyone with 2 doses 3 weeks apart, you have a smaller portion of the population very well protected.

Or NACI is suggesting you can vaccinate lots of people, still maintain very good protection, then go back around & top everyone up for longer protection.

We don’t have the clinical trials we’d like to be 100% on the latter. That’s why there’s some debate on the best option going forward.

But we only have the data we have and need to make a call.

Extending doses appears to be a reasonable option.