The purpose of this website is to document and analyze over time the number, severity, and scope of adverse reactions associated with the COVID-19 vaccines, as reported by the CDC’s passive surveillance system, known as the Vaccine Adverse Event Reporting System, or VAERS. 

Regarding the VAERS system, the CDC has stated the following:

• It is national in scope and serves as an early warning tool for safety problems related to vaccines.  
• VAERS reports can be submitted voluntarily by anyone, including healthcare providers, patients, or family members.  
• Underreporting is one of the main limitations of VAERS, whereby only a fraction of all adverse effects are ever reported.
• A report to VAERS generally does not prove that the identified vaccine(s) caused the adverse event described.  

The VAERS website is available at: https://vaers.hhs.gov/index.html 

[Also note that according to a 2011 Study (see page 6), fewer than 1% of adverse reactions are actually reported to VAERS]

Process:

The CDC publishes new data to its VAERS website every week on Fridays.  All of the VAERS data is available to download as comma-separated value (.csv) files here: https://vaers.hhs.gov/data/datasets.html.  This data goes all the way back to 1990 and includes both domestic and foreign reports of adverse events. Data for this website is also kept up-to-date on a weekly basis to stay in sync with VAERS.  Downloaded data is imported into a relational database without alteration to preserve integrity of the original data, despite many obvious errors and inconsistencies in the data itself. Reports are generated weekly which summarize the data.

Document describing how the VAERS data is structured is here: https://vaers.hhs.gov/docs/VAERSDataUseGuide_November2020.pdf