evidence: Vaccines protect children from these diseases, some of which can lead to hospitalization or even worse. "For example, pertussis (whooping cough) can be a very serious and sometimes fatal disease in infants," says Dr. Patt. But vaccinating infants and expectant mothers against this disease significantly reduces that risk. [...] Failing to Vaccinate Gives New Life to Old Diseases [...] Both the WHO and the U.S. Department of Health and Human Services say that vaccines are one of the most successful and cost-effective disease prevention measures available to society, but vaccine delay or hesitancy threatens to undermine this. For the unvaccinated, their lack of protection from highly preventable diseases is coupled with other issues that vaccinated children and adults don’t have to worry about, such as: