The virus mutates quickly so the vaccine can't be expected to be as effective at new variants compared to the variants it was designed to combat.

> Or are you claiming the boosters have been upgraded with latest variants?

Ok, what would YOU do if you ran Pfizer or Moderna?

1. ship v1.0 of your vaccine with mRNA designed for the original COVID variant

2. modify your vaccine to be effective against the delta variant?

As expected, here is a joint statement from Pfizer and Moderna stating exactly that. [1]

[1] https://www.pfizer.com/news/press-release/press-release-deta...

Boosters are given to improve immune response so the idea is that you improve the immune response so vaccinated people generate more antibodies against an active infection and you get less breakthrough cases.

It’s easy to find the answer to your question. One does not have to deliberately wallow in ignorance.