You are wrong. mRNA covid vaccines don't "only work for 90-180 days". First of all, you need 3 shots to get fully vaccinated in the first place. This is one shot more than the original approved plan, but a very common thing about vaccinations. I got 3 measels shots for example. This has to do with how the immune system works, repeated shots cause different effects which lead to improved immunity.

Also, we are facing very different variants. With the original strain and the first variants, the vaccines would have done their job with just 2 shots and we might even have achieved herd immunity. But delta and especially omicron did happen. Still, with 3 shots, the vaccines against the first strain are still excellent in protecting against severe disease and there is no indication yet that this protection is dropping significantly over time.

To stress this: we are talking about effects due to the nature of the human immune system and the virus mutations. There is no indication what so ever, that the mRNA technology produces shorter lasting immune responses. Quite the contrary, the mRNA vaccines are the ones which proved the most efficient against SARS-Cov-2.

AIDS and COVID are extremely different.

If you are exposed to COVID but got the vax a year ago, you’re likely to have symptoms. You probably don’t actively have antibodies. But that’s okay! You might have some symptoms, in fact they might be severe, but given enough time your immunity will ramp back up, and you still will clear the virus.

If you clear HIV after a week or two, that is a HUGE win for you.

I don't know anything about vaccines or their validity, but even then, the current solutions are a shot once a month or PrEP every day... so twice a year sounds pretty great to me?