Yes, one of the flu strains this year has mutated since this year's vaccines were created. It mutated over the Summer. HOWEVER, it is still absolutely worth getting the flu vaccine. It will still offer some protection: it still reduces the likelihood of very serious illness, and it reduces the chances of added complications and the need for hospitalisation should you come into contact with it. The flu strains from year to year are different.
This year's flu vaccine was made early in 2025. The World Health Organisation has the tricky task of trying to figure out which variations of the flu the populations need protection from, and then the vaccine has to be created, tested, and all before it's distributed in time for Winter.
Flu vaccines NEVER guarantee that any recipient will have 100% protection. The goal is to reduce the severity of illness, reduce the duration of illness, and in doing so, this in turn also helps reduce the spread.
Flu can also be asymptomatic in some people, and also present to varying degrees of mildness in others, leading folks to think that they actually just have a cold virus.
Although a flu virus can be mild in one person, the next person whom they pass it on to could end up in a catastrophic situation, particularly if they have a compromised immune system, or unfortunately, in some cases, otherwise healthy people are just very, very unlucky.
It takes up to 14 days for the flu vaccine to become as effective as it ever will be in the human body. If you get a vaccine and feel ill shortly after, it is likely you had already contracted the flu virus before the vaccine.
In short, it is absolutely worth getting the flu vaccine to give yourself and everyone you come into contact with the best chance of being as well as you could possibly be, should you come into contact with one of the flu strains.