The FDA today approved new, updated COVID vaccines from Pfizer, Moderna and Novavax.
Details here: FDA approves updated COVID-19 shots with some restrictions for kids and adults
Officially said to be "shipping immediately." Where I live (Seattle), multiple locations of the big national chain pharmacies are showing availability beginning on Thursday 4 September (in some locations further east, I'd expect some places might have it as soon as tomorrow, probably more widely available by Saturday or Sunday).
IME based on previous years, the initial appointment slots turned out to be a conservative estimate, and first shots actually became available for walk-ins or same-day appointments several days before the official "first" scheduled appointments (IIRC, on a Saturday). The long holiday weekend might impact that kind of early availability, but if you want to get the jab ASAP, one can now sign up for a September 4 appointment, and if you can get it earlier, cancel the 9/4 slot after you've been poked.
As a reminder, the greatest immune response is said to take about 2 weeks fully to ramp up to maximum protection.
I'm leaving for a trip to Italy on 9/15 so this early shot is what I've been looking for (and I'll be seeing if I can get it a few days early). YMMV.
Lets keep the comments in this thread focused so it doesn't get wiped out.