No vaccine has been proven to be 100% effective in preventing infection or transmission. While vaccines are incredibly effective and have significantly reduced the incidence of many diseases, they do not offer complete protection for everyone. For example, the smallpox vaccine is one of the most effective vaccines ever developed, but even it did not achieve 100% efficacy12.Vaccines work by stimulating the immune system to recognize and fight specific pathogens, but individual responses can vary due to factors like age, health status, and genetic differences. This is why some people might still get infected even after vaccination, although the severity of the disease is usually much reduced2.
