I think the main issue is that it’s not difficult to create a vaccine resistant variant, modifying smallpox is apparently quite easy. Also current vaccines are only effective for around 5 years. I read about this recently, his other book about Ebola is worth a read too:
Do you or your father have deviated septum's? I ask as if you will actually know lol, apparently 80% of us have deviated septum's and there's a direct correlation between that and photic sneezers. I've had it for years but I only found out recently during a routine inspection that I do indeed have a deviated septum.