Vaccines will prevent your pigs from becoming sick 100%,while Air Conditioning will decrease (but not prevent entirely) the chances of your pigs becoming sick.
If there are other non-vaccinated pigs nearby when trying to vaccinate a pig, watch that those pigs are not accidentally vaccinated instead. It's recommended to move the pigs away from each other to prevent mistakenly vaccinating a different pig.
Air Conditioning will need to be replaced when it's broken.