I think that's wrong though. Hypothetically you could have a vaccine engineered alongside the virus and deploy it in secret, or at least using some mode of obfuscation. Not that it would be simple, and not that it wouldn't leak, but it's not an impossible scenario to have a country immunized, I don't reckon.

I mean, look at COVID response, Russia and China both have their own vaccines, what's to prevent them from sliding in something extra to prevent another disease which has been engineered?