(06-10-2021, 07:44 PM)danbrotherston Wrote: Presumably Delta could be tested for using the same PCR methods that all the other variants are selected for.
And presumably there *are* some numbers for it given that the government is making decisions based on us being a "Delta hotspot"...I'm just wondering why we aren't seeing the numbers.
taylortbb mostly addressed it. We got lucky with the other variants in that there was a specific signal in the PCR tests that we're using that correlated strongly with an infection being one of those variants. No such signal exists for Delta. So it looks like the original variant with respect to these tests. But it's also reasonable to infer that if it looks like the original, it probably is Delta these days.
(06-10-2021, 07:44 PM)danbrotherston Wrote: As for boosters...I think that's a misleading term. The term booster, I've usually seen applied to getting revaccinated for diseases 5-10-20 years later, because our immune memory is not infinite. I don't know that we have a specific term for the seasonal flu vaccine we get, which is essentially a new vaccine every year as it protects against a different strain or variant of the flu.
I don't know if we'll need that, I'm not sure anyone does. The beginning of the pandemic, we seemed to see very little change in the virus, but now we seem to be seeing a lot more variants. I'm not sure why, I would have thought variants would be driven mostly by spread, but I didn't think spread was significantly higher now than in the first year of the pandemic. Perhaps our data is better and we are seeing variants more clearly but I don't think so.
In any case, I don't know how different the variants are from each other, especially in terms of their ability to evade our immune defenses (vaccination driven or otherwise), and how that compares with the flu.
I guess there are two questions here: boosters?, and why variants now. I agree that we don't really know if we'll need boosters in the traditional sense, too early to tell.
COVID comes with a natural checksumming technique which slows down the rate of mutation. But there's a guess that the variants arose in immunocompromised people who got convalescent plasma (https://www.scientificamerican.com/artic...e-systems/), so that the virus could be especially good at fighting the immune system in those cases. Sometimes with these things we are just lucky for a while, or there aren't enough chances for something bad to happen yet (remember, exponential growth starts slow).
I think the consensus is that Alpha is definitely more transmissible, and that all known variants are protected against by two doses of the vaccine. Delta seems good at avoiding one dose of the vaccine, which Canada should somehow be worried about, but perhaps there isn't enough Delta and the vaccine administration rate is high enough that people think it'll be OK as long as we continue vaccinating at the current (very fast!) rate.
(06-10-2021, 10:08 PM)danbrotherston Wrote: What I meant about how this compares with the flu is that each year the flu virus has mutated somewhat from previous years (and different strains are more or less prevalent), which is why we have new vaccines every year. But we also know that the previous flu vaccines are somewhat effective for new flu variants each year that the old vaccines were not specifically designed for--which is exactly what we are seeing with COVID. What I don't know is how effective the previous flu vaccine is with new variants. For COVID we actually have some numbers on this. But if we had this number for flu vaccines (and I feel like it must be known, or at least knowable), we could start to get an understanding of how likely we are to need a new vaccine every year based on what policies we already use for flu vaccines.
The flu vaccine just isn't very good, really. (I just got one for Southern Hemisphere winter, though I'm not sure how much flu will actually be an issue this year). We should be able to come up with better flu vaccines in the next few years. The other thing with the flu is that there are a lot of different viruses that cause the flu, so it's possible to target completely the wrong kind of virus. But there's only, to a first approximation, one COVID. And most flus mutate faster than COVID.
ETA: mRNA flu vaccine entering Phase 1 testing this year; also HIV: https://www.biopharma-reporter.com/Artic...-this-year
(06-10-2021, 10:39 PM)taylortbb Wrote: The PCR tests use fluorescing reagents that are keyed to specific genetic sequences. Assuming they're using PCR testing for the mutations, the actual test output is just a yes/no on the N501Y mutation.
Mostly agree. I think it was called an S-gene dropout that allowed differential diagnosis of Alpha, and that was just a happy coincidence, not something people specifically tried for.