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This is Scientific American's 60-Second Science, I am Karen Hopkin. This'll just take a minute.

You’ve probably heard of the whole six degrees of separation thing. It predicts that, on average, you’re no more than six links away from any other person on the planet. Like your roommate runs into a woman whose brother is a writer for Desperate Housewives. Which means you’re only six invites away from having lunch with Marcia Cross’s nannies. The concept stems from the fact that people have social networks, and those networks tend to intersect. But the importance of this “small world” phenomenon extends beyond whose email address you have on your Blackberry. Now scientists think they can take advantage of these networks to design more efficient vaccination¹ programs. According to an international team of physicists², the most effective way to protect a population from disease is to immunize people who have the largest networks. If you can keep the most highly connected people from infecting their friends, neighbors, co-workers, you can halt an epidemic³. And you may only have to vaccinate⁴ half the number of people you would normally. The findings will appear in an upcoming issue of Physical Review Letters. The biggest problem with such a program, people are bound to feel left out when they’re told that they don’t need a shot.

Thanks for the minute for Scientific American's 60-Second Science, I'm Karen Hopkin.