Often parents have concerns about vaccine safety. In licensing vaccines, the U.S. Food and Drug Administration (FDA) has developed scientific criteria for approving vaccines and for monitoring side effects once approval has been given.

Approval of Vaccines

The approval process for a biological product such as a vaccine is based on federal regulations and involves clinical trials in three phases.

Phase One: Studies concerned primarily with learning more about the safety of the product with a few study volunteers.

Phase Two: Studies are usually longer and involve more study volunteers, designed to demonstrate the ability of a vaccine to induce the production of antibodies, as well as to further evaluate side effects and risks.

Phase Three: Studies involving a very large number of study volunteers for longer time. They provide verification that a vaccine is effective in preventing a particular disease as well as information on risks vs. benefits. Clinical trials have been ongoing for years before a vaccine is ever licensed.

After completing the three phases, the manufacturer submits the safety and effectiveness data to FDA in an application for licensure to sell the product. FDA has the responsibility to review the clinical studies data, the facilities to be used and the methods to be used in the manufacture of the product for safety and effectiveness. On average, it takes over five years from the time of application for licensure until FDA approval of a product.

Monitoring Vaccine Safety

After a product is approved for sale, FDA continues to monitor vaccine safety and effectiveness by various means, including on-site inspection of the manufacturing facility. The U.S. FDA staff reviews manufacturers’ testing of vaccines for their safety, potency, and purity. As a protective measure, the U.S. FDA staff may repeat some of the tests themselves.

VACCINE ADVERSE EVENTS REPORTING SYSTEM (VAERS)

This is a national system operated by the FDA and CDC for reporting any possible adverse reactions following immunizations. The system receives reports from healthcare providers, patients, parents or anyone who witnessed or even just heard of a possible adverse reaction that occurred after the receipt of any vaccine. Since 1988, health care providers who give vaccines and vaccine manufacturers are required by law to report certain serious adverse events, and may report any reaction or event.

A VAERS report does not mean the vaccine caused the adverse event. It only means the vaccination preceded the adverse event. VAERS is intended to look for trends and pinpoint the need to investigate further. After vaccines are released for distribution, the FDA conducts reviews of the weekly VAERS reports.

If VAERS is to work, the public should report any serious adverse event following any vaccine given. Report forms may be obtained by calling (800) 822-7967, or contact your clinic or health department.

QUESTION:
How do we know VAERS works?

ANSWER:
VAERS is an effective system for monitoring vaccine safety. Shortly after rotavirus* vaccine became available in 1999, cases of bowel obstruction among some infants who had received the vaccine were reported to VAERS. Although these reports did not provide sufficient evidence to determine if there was a relationship between the vaccine and the bowel disorder, the CDC recommended that use of the rotavirus vaccine be suspended pending further evaluation. The CDC's actions were a direct result of the data obtained through VAERS.

In October 1999 the ACIP recommended that rotavirus vaccine no longer be used because of the strong association between the bowel disorder and the vaccine. Medical experts agree that continued research is needed to clarify the relationship between the bowel disorder and the vaccine.

*Rotavirus is the most common cause of severe diarrhea in infants and young children in the United States.

VACCINE SAFETY DATALINK PROJECT (VSD)

Judgements about whether a vaccine was truly responsible for an adverse event cannot be made from VAERS reports because of incomplete information, such as laboratory results. As a result, researchers are also using large-linked databases (LLDBs) to study vaccine safety. The Vaccine Safety Datalink project is an example of an LLDB. It was established in 1990 by the CDC to study rare side effects associated with vaccines. Four large health maintenance organizations (HMOs) supply the CDC with medical and vaccination records of over six million people (all identifying information is removed to protect patient confidentiality). This large amount of medical data enables researchers to conduct planned vaccine safety studies and examine potential relationships between specific vaccines and adverse events.

QUESTION:
Are there certain vaccine lots that have been associated with more adverse events than other lots?

ANSWER:
Each lot of vaccine undergoes rigorous testing before it is released. FDA officials routinely monitor vaccine lots using VAERS data and other information. VAERS accepts all reports of any adverse event that has occurred following vaccination. Larger lots (i.e. one million doses) are likely to receive more adverse event reports than smaller lots (i.e. 10,000 doses). The fact that there are more reports for a particular lot does not mean that the lot is unsafe, or that the vaccine caused the event. Occasionally, VAERS information has been misinterpreted, leading to unsubstantiated media reports about "unsafe lots" of vaccine.

The FDA has the legal authority to immediately recall a vaccine lot if the number of reports indicate that it may be unsafe, requiring further investigation.

QUESTION:
Do vaccines cause chronic disease, such as diabetes, Crohn's disease, and cancer?

ANSWER:
After decades of vaccine use in the United States, available research shows no reliable evidence proving that vaccines cause chronic illness. Vaccine safety research, including research into theories linking vaccines to chronic diseases, is being conducted on a regular basis in the United States and overseas to assure that the public is receiving the safest possible vaccines.

Occasionally, researchers have published articles about their studies supporting theories about vaccine and chronic illness; however, when other researchers attempt to duplicate their results (the test of good research), they often cannot. Medical conclusions about vaccine safety and the causes of disease must be judged on the quality of the scientific research and evidence.

Because no vaccine is without risk, when medical and public health professionals recommend vaccines for infants and children, they must balance the scientific evidence of benefits, costs, and risks. This balance changes as diseases are controlled or eliminated.