there are different vaccines for H5N1 that already exist, they just have to ramp up production if it starts spreading. too bad like 20-30% of the US will refuse it lol
Probably some minor cross protection but you wouldn't expect much or want to rely on it, and you can't predict how fast the virus will mutate and adapt either
You can always buy some tamiflu from India for $50-100 for peace of mind, at least before antiviral drug resistance develops
I've seen testing up to 10 years after expiry with similar efficacy and a quick google suggests the FDA extended that to 20 years recently
Often causes pretty dreadful vomiting, and it's not clear whether it would be of great benefit in the event of a highly pathogenic flu, but it's the standard treatment for the avian flus
(A meta-analysis did find that it didn't reduce hospitalisation, but it's hard to translate to findings given most people taking Tamiflu are going to be at a high risk)