Fact Checked: Childhood Vaccines Are Carefully Studied—Including with Placebos—to Ensure They’re Safe and Effective

Key Facts

• When a new vaccine is developed, it goes through multiple rounds of research and testing. This process begins with lab research and animal testing, followed by multiple phases of clinical trials to ensure the vaccine is both safe and effective. 
• The vaccine research process involves tens of thousands of study participants, scientists and medical experts. 
• Many childhood vaccines were tested originally in randomized clinical trials that included placebo or comparison groups. If the vaccine is for a disease that currently has no vaccine, the placebo may be saline or another substance known to be safe. If the vaccine is a potential replacement for an existing, older vaccine, the comparator group may receive the older vaccine that has already been tested rather than an inert placebo.
• When a safe, effective vaccine already exists against a disease, giving children in the placebo group no protection against that disease is unethical. Unvaccinated children can contract dangerous illnesses. Parents of children in the placebo group would not know they didn’t get the vaccine and that their child is unprotected. 
• During large polio vaccine trials in the mid-1950s, some children from the placebo group got polio and died.  Today, ethical standards have evolved. No child in a vaccine trial goes unprotected without a very clear scientific and ethical reason. That’s why comparison groups may use an existing vaccine instead of saline. It’s still rigorous science—and it keeps kids safer.
• After testing is concluded, the vaccine manufacturer submits research data to the Food and Drug Administration (FDA), which reviews the vaccine’s safety and effectiveness and determines if it should be licensed. Once a vaccine is licensed, the Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention (CDC) reviews the data and recommends if, how, and when people should receive it. Finally, the CDC, the American Academy of Pediatrics and other groups make a formal recommendation for specific populations, such as children. 
• After a vaccine is in use, the CDC and FDA continually monitor it to make sure it remains safe, and the CDC regularly shares vaccine safety monitoring findings with other federal agencies, the public, health care providers, vaccine manufacturers and advisory committees like ACIP. 
• The CDC and FDA monitor vaccine safety using several different systems. These include the Vaccine Adverse Event Reporting System (VAERS), V-safe, the Vaccine Safety Datalink (VSD), the Clinical Immunization Safety Assessment (CISA) Project, the Biologics Effectiveness and Safety (BEST) System, and others. They also collaborate with government agencies and non-government partners to ensure vaccine safety.
• Vaccines are the safest and most effective way to prevent the spread of infectious diseases, including measles, whooping cough and polio. 

Evidence Snapshot

New vaccines for newly identified pathogens and diseases are tested through randomized controlled trials, comparison groups, and placebos. All existing vaccines have been through this process, as well as ongoing safety monitoring that can identify even very rare side effects. Leading medical organizations including the World Health Organization (WHO) and the American Academy of Pediatrics (AAP) emphasize that childhood vaccines are thoroughly tested to ensure safety and effectiveness.  

Resources for Further Information