I just posted on another thread to explain how evolution works: mutation plus natural selection.
The number of mutations is dependent on the amount of virus in circulation. This is a global pandemic, so there will be a great deal of different mutations. Some will be of little or no concern, some will be a great concern, if more transmissible or to some extent resistant to the vaccine.
So yes, we will likely all need annual booster shots to counter the latest variants. Once the pandemic is over, the virus will become simply endemic. It will be here all the time... but will become less of a concern due to rising immunity within the population, from people who've caught it, from the initial vaccines, and from annual boosters.
The main reason that CV19 has created such chaos is that it is a novel virus, i.e. no pre-existing immunity within the population to slow its progress.