Important: VAERS reports alone cannot determine if a vaccine caused an adverse event. Reports may contain incomplete, inaccurate, or unverified information. Correlation does not equal causation.
A data-driven look at vaccine safety through the lens of 1,983,260 adverse event reports across 104 vaccines spanning 35 years. We present the numbers with context, because raw data without interpretation is easily misunderstood.
Vaccines are among the most studied medical interventions in history. Before approval, they undergo years of clinical trials involving thousands of participants. After approval, multiple monitoring systems — including VAERS — continuously track their safety.
VAERS is one piece of this puzzle. It's an early warning system designed to detect potential safety signals. It's not designed to prove or disprove that vaccines cause specific adverse events. That distinction is critical for understanding the data on this site.
Across 35 years and billions of vaccine doses, VAERS has collected about 2 million reports. The vast majority describe mild, expected reactions:
Serious outcomes represent a small fraction. Of all reports, about 7.2% involved hospitalization and 1.4% mentioned death. But these percentages are not risk rates — they're artifacts of a passive reporting system with known biases. See our denominator problem analysis for why.
Three critical limitations make raw VAERS numbers unreliable for determining vaccine risk:
Different vaccines have different safety profiles. Explore detailed VAERS data for specific vaccines:
When assessing vaccine safety, look beyond VAERS alone:
VAERS is just one tool in a comprehensive safety monitoring ecosystem. It's the most accessible to the public, which is why sites like VaccineWatch exist — to help you understand what the data means.
Vaccine safety is not established once and forgotten — it is monitored continuously across the entire life of a vaccine, from the laboratory through decades of real-world use. Understanding this layered system helps put VAERS in perspective: it is one early-warning component of a much larger apparatus.
Every vaccine begins with preclinical laboratory and animal studies, followed by three phases of human clinical trials. Phase 1 tests safety and dosing in a small group of volunteers. Phase 2 expands to hundreds of people to refine dosing and further assess safety and immune response. Phase 3 enrolls thousands to tens of thousands of participants, comparing the vaccinated group against a placebo group to measure both effectiveness and the rate of adverse events. Only after this evidence is reviewed by the FDA — and, for recommendations, by the Advisory Committee on Immunization Practices (ACIP) — does a vaccine reach the public.
Clinical trials, even large ones, cannot detect extremely rare events that occur in fewer than one in tens of thousands of people. That is the job of post-market surveillance, which includes several complementary systems:
This system has repeatedly proven it works. VAERS and its partner systems detected the rare clotting signal after the J&J vaccine, the myocarditis signal after mRNA vaccines, and the intussusception signal after an early rotavirus vaccine — each of which led to updated guidance or product changes. For a candid look at what VAERS can and cannot do, see is VAERS reliable? and our methodology. You can also explore the underlying reports in the VAERS database and review vaccine-specific side effects guides.
Vaccines undergo rigorous testing before approval and are continuously monitored through systems like VAERS. While no medical intervention is 100% risk-free, the scientific consensus is that approved vaccines are safe and effective. VAERS data shows that the vast majority of reported adverse events are mild and self-limiting.
VAERS is an early warning system that detects potential safety signals. It collects reports of adverse events after vaccination, but reports alone don't prove causation. VAERS is valuable for identifying patterns that warrant further investigation, not for determining whether vaccines cause specific adverse events.
As of 2026, VAERS contains 1,983,260 reports across 104 vaccines spanning 35 years (1990-2026). The vast majority of these reports describe mild, expected reactions like injection site pain, fever, and fatigue.
COVID-19 vaccines were administered to hundreds of millions of people in a very short timeframe during a period of intense public scrutiny. This led to dramatically higher reporting rates — a well-documented phenomenon called stimulated reporting. More reports does not mean more risk per dose.
Vaccine safety is monitored through a layered system. Before approval, vaccines go through preclinical testing and three phases of clinical trials. After approval, VAERS provides early warning signals, the Vaccine Safety Datalink (VSD) compares outcomes in vaccinated and unvaccinated people using electronic health records, the Clinical Immunization Safety Assessment (CISA) project offers expert case review, and the FDA's BEST system runs large-scale active surveillance. The ACIP reviews this evidence to guide recommendations.
No. Report volume is driven mainly by how many doses were given, public awareness, media attention, and mandatory reporting rules — not by how safe a vaccine is. Because VAERS has no denominator (the number of doses administered), raw report counts cannot be used to compare risk between vaccines.