When the flu spreads person to person, instead of from animals to humans, it can continue to mutate, making it harder to treat or fight, because people have no natural immunity.

CNN: WHO raises pandemic alert to second-highest level

We take note of the fact that the British have said that no immunity deal has been made.

WHITEHOUSE: Press Briefing

U.S. government contractors in Iraq also will no longer have criminal and civil immunity under the plan.

CNN: Iraq raid kills suspect in kidnap-slaying of GI