About VaccineWatch

What is VAERS?

The Vaccine Adverse Event Reporting System (VAERS) is a national early warning system to detect possible safety problems in U.S.-licensed vaccines. VAERS is co-managed by the Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA).

Established in 1990, VAERS collects reports of adverse events (possible side effects) that occur after vaccination. Anyone can report an adverse event to VAERS — healthcare professionals, vaccine manufacturers, and the public. Healthcare providers are required by law to report certain adverse events following vaccination.

VAERS serves as one of several systems used to monitor vaccine safety. It is designed to detect possible signals that may indicate a potential safety concern, which can then be studied further through more rigorous methods.

Why VaccineWatch Exists

The raw VAERS data is public, but it is not easy to use. The official files are large CSV downloads that require technical skill to open, join, and interpret, and the government query tool (VAERS WONDER) is powerful but unintuitive for most people. As a result, VAERS numbers are frequently pulled out of context and shared without the caveats that make them meaningful. VaccineWatch was built to close that gap: to make this important public health dataset searchable, visual, and honestly contextualized for journalists, researchers, patients, and anyone trying to understand vaccine adverse event data.

We believe transparency and context are not in tension. Hiding data breeds distrust, but presenting raw numbers without explanation breeds misinformation. Our answer is to show all of the data while consistently explaining what it can and cannot tell you. Every page carries the reminder that a report is not proof of causation, and our methodology is documented openly so anyone can verify how our figures are produced.

Our Editorial Stance

VaccineWatch is neither pro-vaccine nor anti-vaccine — we are pro-transparency. We do not make vaccination recommendations, and we do not use the data to argue for or against any vaccine. We report the numbers as the CDC and FDA publish them, and we add only the interpretive context that public health agencies and epidemiologists themselves attach to VAERS: that it is a passive, over-inclusive early warning system, and that a report describes a temporal association, not a proven cause. When we discuss known safety findings — such as myocarditis after mRNA vaccines or the rare clotting signal after the J&J vaccine — we describe them the way the underlying science does, including how common or rare they are.

For decisions about your own health or your family's, this site is a starting point for understanding the data, not a substitute for professional medical advice. Always consult a qualified healthcare provider who knows your history. You can read more in our frequently asked questions, our glossary of terms, and our full disclaimer.

Where Our Data Comes From

Every figure on VaccineWatch traces back to the official VAERS public-use datasets published by the CDC and FDA. We combine the three linked files VAERS releases — the report-level data, the vaccine data, and the MedDRA-coded symptom data — joined on each report's unique VAERS ID. We do not add outside data, we do not remove reports, and we do not reweight the figures. The result is a faithful aggregation of the public record. You can explore it yourself through our VAERS database and side effects guides, or read exactly how the numbers are computed on our methodology page.

Data Methodology

VaccineWatch processes raw VAERS data files published by the CDC/FDA. Our methodology includes:

• Data source: Official VAERS CSV data files from vaers.hhs.gov
• Time range: 1990 through February 2026 (the most recent available data)
• Processing: We aggregate raw reports by vaccine type, symptom, manufacturer, state, age group, and gender
• Categorization: Outcomes are categorized based on VAERS-defined fields: died, hospitalized, ER visit, disabled, life-threatening
• No filtering: We include all reports as-is. We do not remove or filter any reports
• No interpretation: We present aggregate counts without making causal claims

Update Frequency

The VAERS database is updated approximately quarterly by the CDC/FDA. We process new data releases as they become available. The current dataset was last updated on February 25, 2026.

Data Processing Pipeline

1. Download — Raw CSV files from the VAERS website (VAERSDATA, VAERSVAX, VAERSSYMPTOMS)
2. Parse — Extract and normalize fields, handle encoding issues and inconsistencies
3. Aggregate — Group by vaccine type, symptom, manufacturer, state, age, gender, year
4. Cross-reference — Link vaccine-symptom pairs, create relationship maps
5. Publish — Generate static JSON files for fast, serverless delivery