Now, a century later, we have flu vaccines(疫苗） that have reduced the severity（严重，猛烈） of epidemics（流行病）.

These vaccines need to be updated every year because the virus changes and new strains emerge.(新菌株出现）

What researchers fear is that a new strain of the virus will develop and cause another pandemic.

Once an outbreak occurs, transmission of the disease will be even faster than before.

An unintended consequence of our improved transportation system will be the speed at which an epidemic can spread.

Experts predict that public health systems will be over whelmed(不堪重负） and unable to react quickly enough.

So the best defense will be to prevent an outbreak from occurring.

This will require global cooperation and the sharing of data.

It may also require changes in how humans interact with (与...的相互作用）animals.

Animals such as birds and pigs carry viruses that may mutate(使突变） into a strain that can infect humans.

Such a new strain could lead to another pandemic well before a new vaccine could be developed.

Since diseases and epidemics don't stop at national borders, this is a global issue requiring global action.

The threat of a global epidemic is another example of why we must learn to live together.