I'm willing to believe the empirical evidence that boosters make a meaningful difference, but I can't figure out intuitively why the same mRNA a third time helps to address this new spike.
So when you get a booster (or a breakthrough infection) your immune system kicks into gear again but now it produces a broader range of antibodies. In addition the number of antibodies produced from the booster is quantitatively much larger than from the first vaccine. So with a booster you end up with more antibodies but also a larger variety of antibodies that can recognize different features of the spike protein (including features that are consistent between variants).
That's my understand at least but I am not an immunologist.
Would/could it not also be the case for exposure to the virus that doesn't result in a breakthrough infection i.e. the body detects it and fights it off successfully? (I daresay you didn't mean to imply that, just checking.)
No. That appears not be the situation. Immunity shortly after the thirds shot is substantially higher than shortly after the second
The question is: too quickly for what? My understanding is that
a) If the goal was optimal immunity in the longer term then yes, it might be overly quick.
b) But if the goal was fighting the raging pandemic that needed urgent actions right now as "the house is on fire", and you have a lot of vaccine doses, then no, maybe not too fast.
Finally, a lot of vaccine courses require more than 2 doses, separated by more than a couple of months. UK standard childhood vaccination schedule for instance. "Polio" is in there 5 times. Polio is a memory, but only because because to this day they don't mess around with vaccinating against it
YMMV. The UK gave out AZ and Pfizer. First at a 12 week interval, then shortened to 8 weeks.
There is a reason for that - what's being deployed is what has been tested. You could work out an optimal schedule, but that might take years of trials, and meanwhile people are dying.
It is extremely common for a proper vaccination regimen to require multiple doses, and it has entirely to do with how the immune system works.
By the way, if there are any actual scientists here that spot some atrocious mistake I've made describing this, please let me know. I find it really interesting to learn about but I'm certainly no expert.
To simplify, Vaccines provide long term protection because the immune system builds infrastructure to rapidly create antibodies after infection cutting days off of the immune response. That’s huge because the virus has less time to replicate in your body. Vaccines use multiple injections to increase how much infrastructure is built and the number of types of antibodies being produced. Also this infrastructure decays over time if you never see the strain again.
However, in the short term your body reacts like it’s infected actually flooding the body with the appropriate antibodies. This isn’t sustainable but can crush most infections before they go anywhere. Kind of a bonus turbo mode which can be really helpful if your say going to treat people infected with the disease.
From what I've read, 2 doses in 8-12 weeks is a small separation, as these things go.
A third dose 6 months after the second is not just a third revision of the lesson (metaphorically), but a more appropriate spacing to re-enforce it.
Having had a more recent jab will mean a higher quantities of antibodies. But more vaccinations also means your body has done more cycles of evolving better targeted antibodies against the threat. I assume that there's a certain level of diminishing return to the second factor, as well as questions about how much the extra work translates against a new variant. But the second effect exists alongside the first.
The flu vaccine is a special case as it’s changed every year.
https://en.wikipedia.org/wiki/Smallpox#Prevention
"Smallpox vaccination provides a high level of immunity for three to five years and decreasing immunity thereafter. If a person is vaccinated again later, the immunity lasts even longer. Studies of smallpox cases in Europe in the 1950s and 1960s demonstrated that the fatality rate among persons vaccinated less than 10 years before exposure was 1.3 percent; it was 7 percent among those vaccinated 11 to 20 years prior, and 11 percent among those vaccinated 20 or more years before infection. By contrast, 52 percent of unvaccinated persons died."
“It is recommended that adults get a Tdap shot for one of their tetanus boosters.” https://www.verywellhealth.com/booster-shots-1298291
It simply reduces the number of injections when you get multiple vaccines at the same time.
No, it is not (just) timing.
"Three doses gives better protection than two doses ever did" (1)
Immune response is very complex (2) and we're not experts; but we should not measure it in just 1 number: that gives the impression that the response is a range from "high alert for this recent threat" through to "threat forgotten" - effectiveness did not last that long.
There are there are other states as well when the threat is "on file" in the immune memory. Another exposure months later influences this process. My guess is that the evolved heuristic is that "a threat that recurs more is worth remembering better".
1) https://twitter.com/PaulMainwood/status/1460191035531878405
2) https://www.theatlantic.com/health/archive/2020/08/covid-19-...
3) https://www.theatlantic.com/science/archive/2021/09/waning-i...
If I had to guess, I would expect another anti-COVID jab in 2022. I expect 1 injection in 2022, maybe in autumn, of a mRNA vaccine, against a strain such as Omicron, that is not original COVID-19-alpha. Not a firm prediction, just a guess at what's IMHO most likely.