The real research behind vaccine safety

The first step happens in a laboratory. Scientists develop a vaccine by looking for an antigen that can help teach the immune system to recognize and fight off diseases.source: ⁴ An antigen is something that alerts your immune system to make antibodies to protect itself from a disease.source: ⁵

Once scientists find the right antigen, they test the potential vaccine to make sure it works safely. Long before anything is tested with volunteers, vaccines are tested in the lab with tissue or cell samples and animal testing. That’s why this step is called the Pre-Clinical Stage.source: ³ The results help scientists understand what responses may occur in humans. They also help us know if is safe to move forward with testing in people.source: ³

Next, vaccines go through clinical trials. There are three main stages of clinical trials, each looking at specific things and studying them in different numbers of people.source: ^2,source: ^3,source: ⁶

Depending on the type of study some stages can be combined, so you may see a Phase 2/3 study. Additionally, studies typically include a control group consisting of people who may receive an FDA-approved vaccine, a placebo, or another substance. There is also sometimes a Phase 4 study that takes place after the FDA approves a vaccine. These studies may be required by the FDA to further look at known or potential serious risks.source: ^2,source: ³

Vaccines for children are generally tested using a step-down approach.source: ³ This means clinical trials generally begin with adults first and then step down in age to teens, then children, then babies.source: ⁶ Clinical trials for children generally focus on finding the right dosage that will give children of all ages the best protection with the fewest side effects.

Once the clinical trials are complete, the FDA’s medical and scientific experts review the data to make sure the vaccine is safe, effective, and the benefits outweigh the risks. The FDA also evaluates information about the manufacturing of the product to make sure it can be made consistently and is high quality. After this evaluation of the clinical and manufacturing information, the FDA decides whether to approve the vaccine for use.source: ³

The United States has one of the strongest vaccine safety nets in the world. Before a vaccine even leaves a manufacturing plant, monitoring has begun:

• Facility Monitoring: The FDA inspects all vaccine manufacturing sites regularly to make sure quality and safety standards are met.source: ³
• Batch Testing: Vaccines are made in large batches called lots. Every single lot of vaccines is tested by the manufacturer to make sure the vaccine is made consistently. Samples are also submitted by the manufacturer to the FDA to confirm the manufacturer's results. For approved vaccines, no lot can be distributed until the FDA releases it.source: ³

Once the vaccine lots have been released by the FDA, monitoring begins. There are a number of vaccine safety monitoring systems. Each has a slightly different role, but together they create an incredibly strong safety net. Some of the key monitoring systems are:

• Vaccine Adverse Events Reporting System (VAERS): VAERS is a reporting system for adverse events following vaccination. Anyone can make a report to VAERS, and those reports are publicly available for anyone to read. Experts review the reports to see whether there is a potential pattern. If they find one, they investigate to determine whether an adverse event is related to a vaccine. It’s important to remember that the reports are not proof of a vaccine adverse event. Experts must examine the issue to determine if the adverse event was related to a vaccine. Learn more about VAERS.
• Vaccine Safety Datalink (VSD): VSD is a network of health care systems that investigate and research vaccine safety. They do this by anonymously monitoring every person in their system who has received a vaccine to see if any reported side effects are related to vaccines. They also investigate any patterns found in VAERS to see whether they are connected to vaccines.
• Clinical Immunization Safety Assessment (CISA) Project: CISA is a network of vaccine safety experts, medical research centers, and other public health and medical partners. CISA gives health care providers answers to complex vaccine safety questions and conducts clinical research to evaluate vaccine safety.
• Biologics Effectiveness and Safety (BEST) System: BEST is a system that uses multiple high quality data sources to evaluate the safety and effectiveness of vaccines and other biological products.

In addition to these overarching safety systems, there are other more specific safety systems including:

• V-safe
• The National Healthcare Safety Network
• FDA’s Sentinel Initiative

Finally, there is also ongoing vaccine safety research.source: ⁸