Using different examples, this section examines what it means when we ask the question “Are vaccines safe?” and describes the systems in place to detect rare side effects.

People often consider vaccine dosing in the context of medication dosing, but this concept differs between vaccines and medications. This section describes the differences and answers common dose-related questions.

What is a fever? Why do children get fevers after vaccinations? Should I treat my child’s fever?

Some people concerned about vaccine safety wonder whether vaccines can enter the brain and cause neurological conditions. In order to affect the brain, vaccine components would need to reach the brain. Importantly, our brains are protected by a barrier, called the blood-brain barrier (BBB), which keeps foreign substances from entering the brain.

Antibody-dependent enhancement (ADE) occurs when antibodies created during an immune response worsen responses to future encounters with the pathogen. Both diseases and vaccines can occasionally cause ADE; vaccines that led to ADE are no longer in use.