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This is Scientific American's 60-Second Science. I'm Karen Hopkin. This will just take a minute.

When it comes to flu shots, the more the merrier. Happily, that doesn’t mean you need to get jabbed more than once. What it does mean, according to two reports in the Public Library of Science journal Medicine, is that the vaccines¹ are more effective when more people get them. Because each vaccinated² person is like a roadblock that cuts off further infections.

In the fall of 2000, Canadians launched a unique vaccination³ scheme. Instead of targeting the people most at risk—children and seniors—they offered everyone in Ontario a free flu shot. They even gave them out at the local mall. Now, scientists in Toronto have analyzed⁴ the results of that experiment. They compared what flu season was like in Ontario before and after the year 2000. And they found that the universal vaccination program resulted in fewer flu-related deaths, and fewer trips to the doctor’s office and the hospital.

But people over 75 didn’t seem to benefit. And now Dutch scientists say that one thing that could help seniors is fully⁵ immunizing nursing home staff. Their mathematical study showed that keeping the staff flu-free could in turn cut infections in the residents by more than half. So roll up your sleeve, if not for yourself for your neighbors and your grandpa.

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