Phew. Here's my 2 cents as a scientist with a little knowledge of immunology...
Before Covid, there were already 4 human coronaviruses in circulation. We have ALL had ALL 4 of these coronaviruses in our lives, each multiple times. They cause cold symptoms, and have been around a long time. After we get one, we get partial immunity from that one, which then fades over time, and we get it again. Do these 4 coronaviruses kill people? yes they do! Very old and sick people and immunosuppressed people.
And that is all pre-covid.
There is some evidence that one of the 4 popped up in 1890 or so, source unknown, and caused the global pandemic that killed millions (and might have caused the great economic panic that is considered worse than the great depression). Then once everyone had been exposed, the deaths tapered off, and it just joined the other 3 already in circulation.
As for covid... it looks a lot like the other 4 coronaviruses. The other 4 have been evolving and developing variants for a long time, and have seldom caused deaths in people whose immune systems have seen the earlier versions. Covid will probably just turn into #5 eventually.
All these viruses cause head colds, or rarely pneumonia, in people with partial immunity. There are not a lot of antibodies in nasal mucus, so the virus gets in, infects some cells in your nose, gets sneezed out and its done its job, reproducing and spreading. And your immune system then goes in and wipes out your infected cells (and causes the cold symptoms in the process). Normally, if this virus tries to spread beyond your ENT, the antibodies grab it, and prevent the virus from infecting your vital organs. BC your antibodies are in your blood, not your nasal mucous.
So, now if an unvaxxed person gets covid and has no antibodies, that virus can run rampant through their whole system, infecting all their organ systems (and getting deeper into the lungs) and their brain, causing all kind of havoc. Death or long-term disability.
So what the vaccine (and booster does) is (1) give you antibodies (which fade after 6-18 mos) and (2) gives you T-cells (which never fade, but need some time to wake up and fight the infection). You have two lines of defense.
This is why the vax is not perfect in preventing ENT infections from covid. And the same reason there are no vax's for 'the common cold', bc there are few antibodies and T-cells in nasal mucus. And with the ENT infection you have 'symptoms'. BUT the same vax WILL protect you getting worse complications. Natural infection (if it doesn't kill or disable you first) will give you both antibody and T-cell immunity. It seems less antibody immunity than the vaccine (so you are more likely to get reinfected and some symptoms), but the T-cell immunity may be better (which means it could be as good at preventing death from organ failure as the vax case).
Bottom line, your immune system is complicated and a wonder that has been saving your azz for decades now, and will hopefully keep doing that in the future. It only struggles with germs that it **has never seen before**, but once it has seen a germ, it does a great job of keeping you alive (but doesn't care about 'symptoms', you can suck it up while its doing its thing). Given this, vaccines are brilliant and completely safe... just tipping off your wonderful immune system before an enemy attack.
Covid vaccines work. People who are vaxxed and boosted get infected by omicron, but their odds of dying are reduced by more than 95%! The complication rate from the vaccine is less than 1 in a million.
Original Covid kills about 1% of the unvaxxed people it touches, Omicron close to 0.3-0.5%. I will take a sore arm and a one in a million chance of getting really sick over a 0.3% chance of dying any day of the week. If you aren't vaxxed, you should be.
