https://www.nbcnews.com/news/amp/rcna122361
The government has given poor guidance on how frequently these booster are recommended to be taken, and it’s nearly impossible to find out how frequently they’re allowed to be taken should the patient elect to do so.
And there’s pretty decent data showing that for the earlier versions, the benefits start to trail off after six weeks and are significantly reduced by 12 weeks.
So if you only want to get it once, it seemed logical to wait if your lifestyle suggests peak personal exposure risk would be November, December, and January (which I assume is true for most Americans who aren’t returning to school in September).
This is also an issue with the flu vaccine. It tends to be insufficient coverage for the full flu season, and many healthcare professionals get it twice. For people who only want to get it once, it’s probably been too soon until just now.