The delivery technology has been in development for ages. The payload was tested for about 1 year. IIRC the formulation was done early 2020 in 2 days.
Re your link, it asserts 'MYTH: If I’ve already had COVID-19, I don’t need a vaccine.'. I have serious doubts that is the case, see the OA.
The flu vaccines have been on a yearly basis update schedule. As an organics kind of guy that never sit well with me, but I knew little about vaccines and the flu damage seemed low enough to not matter. It's just an inactivated virus, I'm going to get it either way. These days I wonder how safe the iterated flu shot really is.