This is an interesting question, that I would be harassed by Twitter and Facebook if I spoke about it on their ‘bought’ platforms.
I am no immunologist, but my theoretical physics leads me to think as follows:
Firstly, my understand is that the doses are given in the following strengths, dose 1 (30), dose2 (50), and boosters (70). So the booster is almost as much as the first 2 doses and is given in one hit too. Maybe this is why so many people (eg Shane Warne) are having heart attacks after the booster.
When you get vaccinated, you develop an response to the S-protein spike (ala Wuhan), so when the coronavirus enters your body, it will be ready with antibodies and T cells to stop the virus from spreading. The SARS-CoV-2 virus has 72 spike proteins.
Ideally this is what we want to achieve with vaccines but nothing is perfect, so it helps most of the time but NOT always. We measure this by the so-called efficacy of the vaccine. Initially the Pfizer vaccine for example had an efficacy against symptomatic (or asymptomatic) illness of up to 90% with an expected efficacy against death of around 95%. Initially it was expected that this immunity would last for 6 to 12 months, minimum said most experts. The spread of the virus mant more people where carrying the disease and as it mutated inside human bodies it generated new variants like alpha, beta, gamma, mu, lambda, etc that started to find ways to bypass the vaccines, and the efficacies of all of the vaccines dropped. I might go into that story another time.
When vaccines came along something else went horribly wrong because people had now become even more complacent. The problem was exacerbated by governments who told people ‘if you are vaccinated you are immune to the virus, you are fully protected’ (a statement which is blatantly wrong). Many governments also gave the vaccinated privileges to force people who were unvaccinated to get vaccinated. They introduced “vaccine Passports” or vaccine passes”. As of this day 30 March 2022, the state of Western Australia still has vaccine passports. The unvaccinated were at one time not allowed to buy any alcohol, and at the moment they cannot buy any precious metals from The Perth Mint. I see no connection between buying alcohol or precious metals with covid19. the situation is so ridiculous that the unvaccinated could enter these premises and mingle with the vaccinated but when it came paying for the goods they were refused. This generated a snobbery and blame that the disease was being spread by the unvaccinated, whereas it is the vaccinated who largely carry and spread the virus. The vaccinated went along with this lie (or many probably believed it) as they were now privileged members of society.
Some of the people who were vaccinated were mandated (actually forced) in order to be able to keep their jobs. They had no choice (no human right) to say, hey, my body, my choice. Even the Australian Human Rights Commission was saying on their website that mandating was from their point of view and they even had ads on their website for where to go to get vaccinated, and encouraging parents to vaccinate their children.
There was a clear media propaganda run by the government to try to force as many people as possible to get vaccinated. It is still not clear to be if there is a hidden agenda behind all of this, such as to digitalize everyone with “vaccine passports”. The idea is basically dead now because of the Omicron variant, mind you the premier of Western Australia Mark McGowan is persisting with this bullshit of medical apartheid. He is actually still mandating the vaccine on most workers, while most other states in Australia and countries around the world have abolished this tyrannical authoritarianism.
Then suddenly along came a variant to replace all other variants because it was so much more infectious than anything before it. We were living in a world of the delta variant. Vaccine complacency and virus pool (a constant large number of infected vaccinated people) allowed the delta variant to mutate with it to generate another 243 new subvariants. The efficacy of Pfizer dropped to 70% for symptomatic illness, and astrazeneca dropped to 40%. Now Vaccines were now even less effective, which meant that the size of the virus pool became even larger. The spike on the coronavirus had now changed away from the original Wuhan S-spike protein (which incidentally is patented by Moderna and proves the coronavirus was made in a lab.). This is why the vaccines had become less effective. But what did governments and people do, they keep injecting with vaccine with the Wuhan S-protein spike). A bit silly really, but that is what happened.
The world was then half blessed by the emergence of a new variants called Omicron