Understanding Vaccine Safety
An interactive guide to the science, impact, and safety of vaccines. Explore the data and learn how vaccinations protect individuals and communities across the globe.
How Do Vaccines Work?
Vaccines train your body's immune system to recognize and fight off harmful viruses or bacteria. This creates a "memory" of the germ without you having to get sick first.
A Harmless Piece
A vaccine introduces a tiny, weakened, or inactive part of a germ (an antigen) into your body.
Building Defense
Your immune system recognizes the antigen as foreign and produces antibodies to fight it.
Creating Memory
Your body remembers the germ. If you're exposed to it in the future, your immune system can quickly destroy it.
The Global Impact of Vaccination
Routine childhood immunizations have dramatically reduced illness and death worldwide, saving millions of lives. The chart below shows this impact, which you can explore by clicking the button.
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Lifetime illnesses prevented in the US (children born 1994-2023).
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Premature deaths prevented in the US (children born 1994-2023).
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Saved in societal costs in the US. That's $11 saved for every $1 spent.
Addressing Common Concerns
It's normal to have questions. Here are the facts behind some common concerns about vaccine safety, based on decades of scientific research.
Fact: No. This is one of the most studied health topics. Numerous large-scale studies involving millions of children have found no link between any vaccine and autism. The 1998 study that started this fear was retracted because it was found to be fraudulent. Leading medical organizations worldwide agree that vaccines do not cause autism.
Fact: No. Ingredients like aluminum and thimerosal are used in tiny, safe amounts. Aluminum is used as an adjuvant to boost the immune response, and babies receive far more aluminum from their daily diet than from vaccines. Thimerosal, a preservative, was removed from most routine childhood vaccines in the mid-1990s as a precaution, and no reliable study has ever linked it to developmental disorders.
Fact: Vaccination is much safer. While getting sick can provide immunity, it comes with serious risks. For example, a natural measles infection can lead to pneumonia, brain damage, or death. A vaccine provides immunity without the risk of severe illness and its potentially life-threatening complications.
Vaccination Across the Lifespan
Vaccine needs change as we age. Explore the importance of vaccination for both children and older adults.
Protecting the Youngest
Childhood vaccines are one of the greatest public health successes. They protect children from serious and sometimes deadly diseases like measles, polio, and whooping cough when they are most vulnerable. High vaccination rates also create "community immunity," which protects babies too young to be vaccinated and people with weakened immune systems.
Routine immunizations have saved an estimated 94 million lives from measles alone in the last 50 years.
A Timeline of Progress
Key milestones in the history of vaccination show a long journey of scientific discovery and public health success.