Mine are already organic. I never vaccinate, I breed for disease resistance. I don't medicate chicks. I rarely have any chicks die unless it's something like the bulb in the brooder went out and some chilled or were smothered. That stopped when I started using reptile heat bulbs and ceramic heater bulbs. Those cheap light bulbs now are horrible.
I quarantine everything new and one time had some 4 month old chicks that were in quarantine a couple of weeks come down sick, lost all but a couple but those 2 are healthy and integrated into the flock. If I had a lot of chicks dying and thought I needed to vaccinate, I would be looking elsewhere for chicks or finding a way to clean up my pens if there was disease there to prevent future outbreaks. I live way out in the country, but there are turkey barns within 6 miles and a poultry egg barn less than a half mile from me. Disease is everywhere, in the wind, carried by wild birds..etc etc. My best line of defense is keeping the flock clean, healthy and not ever going further than just basics to care for chicks, no out of the ordinary care, if they die, the reason may be a poor immune system or some other quality they're missing.
