Lifetime immunity doesn't make much economic sense. If you have a vaccine with people and governments from all over the world begging for you to sell it to them, vaccine as a service seems like a more efficient model than a one-time purchase.
Not for the market leader, and maybe not for number two. But if you're at the end of the pack, nobody buys from you and you look at the 10 billion people market you could get with a lifetime vaccine...
Which is why monopolies are bad. You don't have a pack anymore, and the leader(s) don't have incentive to do much disruption.
