The survivors of Hiroshima and Nagasaki didn't have fallout shelters with proper ventilation. Many got sick and died and many got sick and recovered and many didn't get sick at all. This despite not know anything about what to do in the aftermath of a nuclear strike and despite being in a country whose infrastructure was thoroughly crushed even before the bombings. About 150,000 of them are still alive more than 70 years later.And unless you have a fallout shelter with proper ventilation and amble food an water you will get sick eventually. If you are lucky enough to have those things then there will be plenty of people that are going to want it. And that is where the ugliness sets in. Are you prepared to kill your neighbors? You will likely have to to survive.