COVID-19 Vaccination Development & Safety

How do COVID-19 vaccine clinical trials work?

Vaccine trials are completed in the phases outlined below:

• Research & Discovery: Research is conducted in a laboratory to identify potential vaccine candidates. Through this testing, the vaccine candidate that shows the most benefits moves to the next step.
• Pre-clinical testing: Pre-clinical testing involves laboratory research and testing in animals to determine a vaccine's effectiveness and safety before moving to human trials.
• Phase 1 & 2: Testing occurs in small groups of healthy adult volunteers to identify any safety concerns and gain early information about how well the vaccine works.
• Phase 3: If no safety concerns were identified and the vaccine showed effectiveness, Phase 3 involves testing in larger groups of diverse populations ranging from several hundred to 3,000 people.  For the COVID-19 vaccine trials, grants from health departments enabled researchers to test even larger groups, some totaling more than 60,000. More extensive group testing has helped expedite data collection on side effects, vaccine effectiveness, and how to safely administer the vaccine.
• Phase 4: Phase 4 involves a final review of all clinical trial data, and the FDA makes a final decision for approval. Monitoring doesn't stop after approval – the FDA and regulatory agencies continue to monitor production, manufacturing, vaccine efficacy, and safety.

What is a COVID-19 Emergency Use Authorization?

The first COVID-19 vaccine is being administered under an Emergency Use Authorization, or EUA. An EUA is submitted to the FDA during a public health emergency and allows medical countermeasures, such as vaccines, to be used before completing Phase 3 of the FDA approval process. Post authorization, the FDA, the CDC, and other healthcare agencies closely monitor vaccine safety and effectiveness.  

How safe are the COVID-19 vaccines?

Safety is a top priority during any vaccine approval process. Clinical trials are continually monitored for possible side effects, unexpected health events, or potential safety concerns. Even after FDA approval, the FDA conducts ongoing surveillance on vaccines. It is important to remember that no vaccine is 100 percent effective in preventing disease or 100 percent safe in all individuals despite rigorous and comprehensive safety protocols.

Read more about vaccine safety here: 

CDC Vaccine Safety

Get the CDC's Post-vaccination Health Checker, V-safe. This smartphone-based tool provides personalized health check-ins after you receive your COVID-19 vaccination:

V-safe

Learn more about FDA authorized COVID-19 vaccines:

Pfizer COVID-19 Vaccine Information

Moderna Vaccine Information

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