As soon as babies are born, their immune systems start going to school. They begin learning how to recognize and eliminate tiny invaders—like viruses and bacteria. Basically, they’re learning the ABCs of health.

And let’s be real, babies are constantly exposed to new things. Anything they put in their mouth (which is basically anything that they can grab), or even just the dust they breathe, is like a mini lesson in "How to Identify Antigens 101." They’re basically walking classrooms for germs.

But some of these germs are sneaky—they can cause sickness before the baby’s immune system has even had a chance to study up. That’s where vaccines come in. They give the immune system a little preview of the germ—like a practice test—so it knows what to expect and can fight it off before it gets a chance to cause any trouble.

While vaccines introduce some antigens, babies are exposed to way more from the world around them. The cool part? Modern vaccines use way fewer antigens than the ones from 40 years ago. So, babies get to learn more about diseases with less exposure to the actual germs. It’s like getting an accelerated course in immunity—less homework, better results!

Learn more by watching this video with Dr. Paul Offit with the Children’s Hospital of Philidelphia’s Vaccine Education Center: Do Babies Get Too Many Vaccines?

You can also learn more by reading the following Q & A from Children's Hospital of Philadelphia.