"Lifetime immunity" means that someone is protected from a specific disease or condition for the rest of their life and will not be affected by it again. Full definition
One problem with many vaccines is that they don't provide lifetime immunity and thus require booster shots. (cityofhope.org)
If a cat is lucky enough to recover from this infection, generally no permanent damage is retained and the cat goes on with lifetime immunity. (vin.com)
While no vaccine guarantees lifetime immunity (boosters are required), all house cats should be vaccinated as kittens with the «core» vaccines. (cat-lovers-only.com)