"Flu spreads easily and can cause serious illness which would need to be treated in hospital, " said Dr Hussey.

BBC: Flu jab given at some pharmacies in Wales for first time

When a flu spreads, or an earthquake strikes, or cartels threaten innocent people, it affects lives on both sides of our common border.

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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

When the flu spreads person to person, instead of from animals to humans, it can continue to mutate, making it a tougher strain that is harder to treat or fight off.

CNN: U.S. prepares for possible swine flu epidemic as global cases rise

On a cruise, word of mouth spreads like the flu.

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Instead, it spreads like any other flu: someone sneezes or coughs, spreading the virus to other mammals (humans included) and onto surfaces.

CNN: CDC: Cases of new swine flu strain rising

Instead, it spreads like any other flu -- someone sneezes or coughs, spreading the virus to other mammals (humans included) and onto surfaces.

CNN: CDC: Increase seen in new swine flu strain