Bro
BROO
Mutations are RANDOM. It's not a sure process. It could become WAY deadlier, but less transmissible. It's a roll of the dice.
Meanwhile, vaccines don't guarantee complete immunity. I got a tetanus vaccine when i was 12, and if i cut myself on rust, I can still get tetanus. It's your immunity, and how fast it works is also a roll of the dice. There are 2 kurzgesagt video on it. Before watching it, even I thought the vaccine was not as great as advertised, but afterwards, tying that with what i know about vaccines, it makes sense that it's not a complete shield.
Also what are you, some anti-vaxxer? If you are, that means you won't understand what I said above, in which case nice opinion, unfortunately your mother.