It goes without saying that unvaccinated kids get more vaccine-preventable illnesses. For instance a 2010 study from Kaiser Permanente showed that children who hadn’t received pertussis vaccine were 23 times more likely than vaccinated children to get pertussis.

But there’s another consequence of not getting vaccines. It hurts your child, sure. But it also can hurt other people in your community.

Vaccines are not perfect. Not everyone who receives a vaccine gets 100% protection; and some people in a community are too young to be vaccinated, or have health conditions that prevent vaccination. Those that aren’t immune depend on what’s called “herd immunity” for protection. If just about everyone else is immune, then the diseases don’t circulate, and even those who are not immune are unlikely to come in contact with the disease.

This kind of protection — the herd effect — only works if just about everyone is immune. As soon as the herd fails to maintain a high percentage of immunity, more disease circulates, and more people get sick. Not only do those who chose not to vaccinate get vaccinated get sick, but also those who couldn’t get vaccinated, or those in whom the vaccine didn’t work.

This was just illustrated in a study reported in Pediatrics, looking at non-medical vaccine exemptions in California. Researchers looked at geographic areas where there were clusters to non-vaccinated families, and compared that to geographic areas with clusters of pertussis cases — and as expected, the two overlapped. If you live in an area with a higher proportion of non-vaccinated people, you’ve got a higher risk of picking up pertussis. This risk is increase even if you and your own family are vaccinated.

Though the vast majority of children nationwide receive their vaccines, a small number of vocal pro-disease, anti-vaccine propagandists has managed to scare many parents into becoming hesitant about vaccinations. And the diseases are coming back. Don’t fall for it. Protect your kids, protect yourself, protect your community. Get those vaccines, on time and on schedule.

Roy Benaroch is a pediatrician who blogs at The Pediatric Insider. He is also the author of Solving Health and Behavioral Problems from Birth through Preschool: A Parent’s Guide and A Guide to Getting the Best Health Care for Your Child.