How are vaccines monitored once they’re released for public use?

Short Answer

Vaccine safety is continuously monitored by the Food & Drug Administration (FDA) and the public, including doctors and parents. The FDA tests samples of each vaccine before it can be distributed by manufacturers, and will issue recalls if the batches don’t meet rigorous standards for safety, potency, and purity. The Vaccine Adverse Event Reporting System (VAERS) is a public tool that allows doctors, parents, and patients to report any side effects or reactions to vaccines they experience. The VAERS database then looks for patterns within the data and flags vaccines or ingredients for further testing or monitoring to ensure the highest degree of safety possible.


After a vaccine is licensed for public use, its safety is monitored continually. The FDA requires all manufacturers to submit samples from each vaccine lot prior to its release. In addition, the manufacturers must provide the FDA with their test results for vaccine safety, potency, and purity. Each lot must be tested because vaccines are sensitive to environmental factors like temperature, and can be contaminated during production. During the last 10 years, the FDA has recalled only three vaccine lots: one was mislabeled, another was contaminated during production, and the third was recalled after the FDA discovered potential manufacturing problems at a production plant. [7]

While clinical trials provide important information on vaccine safety, the data are somewhat limited because of the small number (hundreds to thousands) of study participants. Rare side effects and delayed reactions may not be evident until the vaccine is administered to millions of people. Therefore, the federal government established a surveillance system to monitor adverse events following vaccination. This project is known as the Vaccine Adverse Event Reporting System (VAERS). More recently, large-linked databases containing information on millions of individuals have been created to study rare vaccine adverse events.[13]


Vaccine Adverse Event Reporting System

While VAERS provides useful information on vaccine safety, the data are somewhat limited. Specifically, judgments about causality (whether the vaccine was truly responsible for an adverse event) cannot be made from VAERS reports because of incomplete information. VAERS reports often lack important information such as laboratory results. As a result, researchers have turned more recently to large-linked databases (LLDB) to study vaccine safety. LLDB allow scientists to access the complete medical records of millions of individuals receiving vaccines (all identifying information is deleted to protect the confidentiality of the patient). One example of an LLDB is the Vaccine Safety Datalink (VSD) project described below, which is coordinated by CDC. Studies conducted using LLDBs like the VSD are also known as post-marketing research or phase-four clinical trials. [1]

The National Childhood Vaccine Injury Act of 1986 requires health-care providers to report certain adverse events that occur following vaccination. As a result, CDC and the FDA created the Vaccine Adverse Event Reporting System (VAERS) in 1990. VAERS provides a mechanism for the collection and analysis of adverse events (side effects) associated with vaccines currently licensed in the United States. Adverse events are defined as health effects that occur after immunization that may or may not be related to the vaccine. VAERS data are monitored continually to detect unknown adverse events or increases in known side effects. [19]

In 2008, VAERS received more than 25,000 reports of adverse events in the United States. Of those, 9.5% were reported as serious events (causing disability, hospitalization, life-threatening illness, or death).[1] Anyone can file a VAERS report, including health-care providers, manufacturers, and vaccine recipients or their parents or guardians. [19] Those who have experienced an adverse reaction following immunization are encouraged to seek help from a health-care professional when filling out the form.

VAERS forms can be obtained in several ways. Each year the form is mailed to more than 200,000 physicians specializing in pediatrics, family practice, internal medicine, infectious diseases, emergency medicine, and obstetrics and gynecology. In addition, copies are sent to health departments and clinics that administer vaccines. The VAERS form requests the following information: the type of vaccine received, the timing of vaccination, the onset of the adverse event, current illnesses or medication, history of adverse events following vaccination, and demographic information about the recipient (age, gender, etc). The form is preaddressed and stamped so it can be mailed directly to VAERS. To request a VAERS form or assistance in filling in out, call 800-822-7967.[19]

A contractor, under the supervision of FDA and CDC, collects the information and enters it into a database. Those reporting an adverse event to VAERS receive a confirmation letter by mail indicating that the form was received. This letter contains a VAERS identification number. Additional information may be submitted to VAERS using the assigned identification number. Selected cases of serious adverse reactions are followed up at 60 days and one year post-vaccination to check the recovery status of the patient. The FDA and CDC have access to VAERS data and use this information to monitor vaccine safety and conduct research studies. VAERS data (minus personal information) are also available to the public. [19]

The importance of vaccine safety will continue to grow throughout the 21st century. The development and licensure of new vaccines will add to the already complicated immunization scheduling. Scientists may also perfect new ways of administering immunizations including edible vaccines and needleless injections. However they are formulated or delivered, vaccines will remain the most effective tool we possess for preventing disease and improving public health in the future.

Citations for this page

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