If you give people a vaccine that doesn't work, or worse a vaccine that does more harm than good (or appears that way), then you explode the anti-vax movement i

If you give people a vaccine that doesn't work, or worse a vaccine that does more harm than good (or appears that way), then you explode the anti-vax movement into the rule rather than the exception. No subsequent vaccine, even an effective one, would be tolerated. It's not worth getting wrong.