Vaccine Safety
Vaccines are held to the highest standard of safety, and CDC monitors vaccines in use for safety and effectiveness.
Vaccines are our best defense against infectious diseases, but vaccines may not be 100% safe or effective. Our bodies react differently to vaccines. Some people may have side effects after vaccination, and some may not be completely protected from disease. Scientists are constantly working to develop safer, more effective vaccines.
Vaccines, like any medication, can cause side effects and pose risks. There may be rare side effects or delayed reactions that may be detected only after the vaccine is given to millions of people after it is licensed and recommended. However, a decision not to immunize a child also involves risk. It is a decision to put the child and others who come into contact with him or her at risk of getting a disease that could be deadly.
Testing Vaccines before Licensing
Vaccines must be licensed by the U.S. Food and Drug Administration (FDA) before they can be used in the United States. Before the FDA approves a vaccine, that vaccine must be tested extensively (typically in thousands to tens of thousands of people) to ensure it is safe. The tests manufacturers must perform on each lot are spelled out in the product license application. FDA also makes certain that the manufacturing facility can properly produce the vaccine before it is licensed for use by the agency.
Monitoring Vaccines after Licensing
After a vaccine is licensed, its safety is monitored continuously in several ways. FDA requires the manufacturer to test samples from each lot for safety, potency and purity, and FDA also carries out its own tests.
CDC and FDA jointly manage the Vaccine Adverse Event Reporting System (VAERS), a voluntary reporting system used by the patients, manufacturers, public health officials, and healthcare professionals to report potential adverse effects from vaccinations. Using reports from VAERS, CDC scientists can look for patterns that suggest a side effect is actually caused by the vaccine. Through its Vaccine Safety Datalink (VSD) project, CDC also studies associations between vaccines and possible side effects. This project uses the combined resources of many healthcare providers and systems to search medical records of 8.8 million members of participating managed care organizations, and watch them for possible side effects of vaccination.
Why It's Important to Monitor Vaccine Safety
The most important reason to monitor vaccine safety after a vaccine is widely available and widely used is to detect reactions that are so rare they are not found during testing before a vaccine is licensed. Monitoring also helps ensure that new vaccines are safe for groups such as the elderly, those with chronic medical conditions, and pregnant women, who may not be included in pre-licensing testing. Usually, monitoring vaccine safety finds that there are no serious reactions that have been missed in earlier testing of a new vaccine. If new serious reactions are discovered, CDC shares information and tries to identify characteristics that may increase risk for the side effect.
Consider the combination mumps, measles, rubella, varicella (MMRV) vaccine. As part of routine safety monitoring for new vaccines, in 2007 CDC implemented a postlicensure vaccine safety study for the combined MMRV vaccine in children aged 12–23 months, the age when the first dose of combined MMRV or measles, mumps, rubella (MMR) and varicella vaccines is recommended.
The following shows key activities performed by CDC, FDA, and the Advisory Committee on Immunization Practices (ACIP) concerning MMRV vaccine.
February 2008:
- ACIP reviewed preliminary information on the risk of febrile seizures after vaccination with combination MMRV vaccine (ProQuad®).
- ACIP voted to remove its previous preference for administering combination MMRV vaccine over separate injections of MMR vaccine and varicella vaccine.
- ACIP also recommended that a MMRV Vaccine Safety Working Group be formed.
- FDA reviewed postmarketing data and the MMRV package insert was updated. The revised package insert includes new and evolving information on the risk of febrile seizures after MMRV vaccination.
March 2008:
- Updated ACIP recommendations regarding MMRV vaccine use were released in CDC's Morbidity and Mortality Weekly Report (MMWR).
- The MMR and varicella Vaccine Information Statements were updated.
June 2008:
- The ACIP MMRV Vaccine Safety Working Group was formed to evaluate the safety information related to MMRV vaccine and consider options for future MMRV vaccine recommendations
July 2008-present:
- The ACIP MMRV Vaccine Safety Working Group is completing its tasks and will present the findings from the safety and policy evaluations at a future ACIP meeting.
CDC and FDA will continue to monitor the safety of MMRV vaccine. They will also communicate updates and take any further necessary actions based on the findings
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