9 dangerous diseases that could be prevented by vaccines within the next decade, from HIV to cancer

One of the best defenses we have against viral infections is the vaccine.

Vaccines prime the body's immune system to fight an incoming infection; they've been credited with the widespread eradication of smallpox and the near-eradication of polio.

There have been many major advances to vaccines since their inception in the 1700s, but there are still many diseases for which no vaccine exists.

At the same time, researchers are finding ways to use the immune-system-triggering effects of vaccines to tackle unexpected diseases, such as cancer and drug addiction.

To get approved, vaccines need to show that they're both safe and effective at preventing diseases or - if they're used therapeutically - at activating the immune system to go after existing diseases. That process can take years or even decades.

Here are nine vaccines currently in development that could dramatically change how humans live.