Vaccine safety tip sheet

When reporting on vaccines, it can be helpful to explain in your coverage how we know they are safe and effective. Here are the basics of vaccine approval and monitoring.

For the most part, the process of approving a vaccine works the same as any drug.

• Preclinical studies take place in petri dishes in a research lab and in animals. They try to determine the way a drug works, whether it appears to prevent the disease (in rodents), and if it seems generally safe.
• After multiple preclinical studies, clinical trials have three stages and take place under the supervision of the Food and Drug Administration (FDA).
  • Stage 1 clinical trials involve 20-100 human participants and focus on safety and side effects. They don’t try to determine whether a vaccine works, only whether it’s safe to test on more people.
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    Stage 2 clinical trials involve several hundred participants. They aim to gather more safety information and determine whether the vaccine causes an immune response in people.

  • Stage 3 clinical trials involve thousands of participants. This is where researchers establish how effective the vaccine is at preventing illness or disease transmission, as well as potentially identifying less common side effects.
• Only after all three stages have completed can a vaccine manufacturer apply to the FDA to approve the vaccine.
• Once a vaccine has been approved by the FDA as safe and effective, the Centers for Disease Control and Prevention (CDC) make recommendations for use of the vaccine.
• This process typically takes years. Emergency use authorization involves these exact same steps, just more quickly.

After a vaccine is approved, post-licensing monitoring systems continue to look out for rare side effects.

• The Vaccine Adverse Event Reporting System (VAERS) allows individuals, clinicians, and vaccine manufacturers to report any possible side effects experienced after receiving a vaccine.
  • Reporting an event to VAERS does not mean the event was caused by the vaccine, just that it happened after receiving a vaccine.
  • Vaccine manufacturers have to report all possible side effects they learn about, health care professionals are required to report specific side effects, and individuals can report their experiences with possible side effects.
  • VAERS doesn’t determine whether a vaccine causes a side effect. It identifies patterns for government agencies and researchers to investigate, including possible new and rare side effects, but also things like bad batches of a vaccine, or vaccines that clinicians have a lot of difficulty administering.
• When a pattern of possible side effects is identified through VAERS, the Vaccine Safety Datalink (VSD) conducts research to determine whether it was caused by a vaccine.
  • When a potential concern is identified, researchers pull thousands of electronic health records from 11 health systems around the country.
  • They run several different types of analyses to determine whether the rate of that side effect is higher in people who got the vaccine than those who didn’t, which would suggest that the side effect is due to the vaccine.

If post-licensure monitoring reveals a safety concern, the vaccine can be pulled from the market. This has happened before, with a Lyme disease vaccine, a rotavirus vaccine, and specific types of measles and intranasal flu vaccines.

Further reading: VAERS and the path to vaccine approval.