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How do we know new vaccines have been researched enough?

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Vaccines go through many steps before being available to the public. There are three important things to know about new vaccines:

  1. Vaccine science builds on decades of research across many different vaccines. Our knowledge about vaccines is based on evidence that is developed systematically, with studies first being reviewed by experts at the U.S. Food and Drug Administration (FDA) and then by outside experts (as part of the Advisory Committee on Immunization Practices [ACIP]) following approval. There are many steps in place to ensure that new vaccines are safe and that they work. Vaccine science is not new—scientists have been researching many of today’s vaccines for decades.source: 1,source: 2,source: 3 And they use that research to help develop new vaccines.
  2. Vaccine clinical trials and several other systems monitor for any long-term side effects.source: 3,source: 4 Also, we know from years of research across different vaccines that long-term side effects are rare.source: 5 Learn more about this in the Deep Dive section below.
  3. Misinformation about new vaccines is very common. Myths and untrue information have been repeated for decades. That’s nothing new. But as scientists develop new vaccines, and as more channels for information become popular, misinformation is much more common and widespread.source: 6,source: 7

Key Evidence

  • Typical vaccine development can take years. There are many steps in development that ensure the safety of new vaccines.source: 8,source: 9 Clinical trials study the vaccine in thousands of people to understand the vaccine’s effectiveness and any side effects and the correct dose.source: 10 Finally, the vaccines are rigorously evaluated by experts at the U.S. Food and Drug Administration (FDA) to decide whether to approve them for use.source: 11
  • The U.S. vaccine “safety net” is one of the best in the world. There are a number of safety systems that monitor the safety of vaccines.source: 4,source: 12
  • History shows us vaccines are safe.source: 9 Many people do not think vaccines are safe because of false information that gets spread. But we only have to look around to know that vaccines are safe and that they work. Billions of people around the world have safely received vaccines. As a result, many diseases that once killed thousands have become uncommon.source: 1,source: 13
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A Deeper Dive: Learning about long-term side effects

Some parents want to wait for a couple of years to give their children a new vaccine, because they believe it can take that long to know all side effects.

But here’s a fact: Most side effects occur within a few weeks of vaccination and go away on their own within a few days. Usually, these are known before a vaccine is approved for public use because common side effects are found during clinical trials.source: 11,source: 14

There are more than 60 different approved vaccines in the United States that protect against more than 25 different diseases.source: 15 Assuming many of these vaccines were studied for 5 years or more, and if the researchers for these vaccines only worked a 40-hour week (and most work more), that is more than 3.1 million hours of research. And this research tells us that long-term side effects from vaccines are rare.source: 5

Back to the common questions

More information

Still have questions? Talk to your child’s doctor, nurse, or pharmacist.

Sources

  1. WHO: A Brief History of Vaccination
  2. HHS: Vaccine Safety
  3. CDC: How Vaccine Safety Monitoring Works
  4. CDC: Vaccine Safety Systems
  5. FDA: Vaccines Protect Children From Harmful Infectious Diseases
  6. KFF: KFF COVID-19 Vaccine Monitor: Media and Misinformation
  7. HHS: Confronting Health Misinformation
  8. Johns Hopkins Coronavirus Resource Center: Vaccine Research & Development
  9. CDC: How Vaccines are Developed and Approved for Use
  10. FDA: The Path for Vaccines
  11. FDA: Vaccine Development – 101
  12. CDC: About CDC’s Vaccine Safety Monitoring Program
  13. ACF: The History of Vaccines and Immunization: Familiar Patterns, New Challenges
  14. CDC: Pink Book: Vaccine Safety
  15. CDC: Vaccines By Disease
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