Most newborns with illnesses like whooping cough and influenza catch it from someone inside the home. That's why it's important for those closest to a newborn—such as parents, grandparents, and siblings—to stay up-to-date on shots.

"When adults get vaccinated, it curbs the spread of disease to infants and children who are either too young to be immunized or not yet fully protected," says Anita Chandra-Puri, MD, a spokesperson for the American Academy of Pediatrics (AAP) and a pediatrician at Northwestern Memorial Physicians Group in Chicago.

This strategy is called "cocooning," says Matthew Daley, MD, a pediatrician for Kaiser Permanente in Colorado and a researcher who studies vaccine topics. "Cocooning is protecting the baby by immunizing the people around [them], like the parents, grandparents, and other kids (but hopefully, they're already caught up with their vaccinations)," Dr. Daley says.