Vaccines are poisonous. There's a good reason they make you feel sick. And Not all of them work.
And where they can make good guesses...there's a lot to making a good one.
I'd dare say that there are at least 5 different ones, in different countries, being tried out right now. Eventually they will be ready for stage two, then stage three trials.
Getting the dosing right and finding all the interactions with medicines and other ailments takes a while.
Doesn't do any good to kill both virus and patients. Kinda want patients to live...they tend not to pay their bills when they die.
And these studies have to be done double blind...meaning that no one knows (including doctors, researchers, and nurses)who is getting the test vaccine vx regular flu vaccine.