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.
Key events in the history of vaccine safety monitoring in the United States — from early manufacturing disasters to modern surveillance systems. This timeline shows how today's safety infrastructure was built, often in response to problems.
Improperly inactivated polio vaccine from Cutter Laboratories caused 40,000 polio cases, 200 children paralyzed, and 10 deaths. Led to stricter manufacturing oversight.
Explore related data →Mass swine flu vaccination campaign halted after ~450 cases of Guillain-Barré Syndrome detected. Demonstrated the need for ongoing safety monitoring.
Explore related data →Congress created the National Vaccine Injury Compensation Program (VICP) and mandated reporting of certain adverse events. Foundation of the modern vaccine safety system.
Explore related data →The Vaccine Adverse Event Reporting System launched as a joint CDC/FDA program. Now contains 1.98M+ reports and is the primary public database for adverse event monitoring.
Explore related data →Andrew Wakefield published a fraudulent study linking MMR vaccine to autism. The paper was retracted in 2010 and Wakefield lost his medical license, but anti-vaccine movements grew.
Explore related data →First rotavirus vaccine (RotaShield) withdrawn after VAERS detected intussusception risk — about 1 in 10,000 infants. A success story for the safety monitoring system.
Explore related data →Gardasil approved for cervical cancer prevention. Generated significant reports in VAERS, with fainting (syncope) identified as a notable side effect in adolescents.
Explore related data →The Lancet fully retracted the 1998 MMR-autism study. Multiple large studies found no link between MMR and autism. Wakefield was struck off the UK medical register.
Explore related data →VSD expanded to cover ~12 million people across 9 healthcare organizations, enabling active surveillance that complements VAERS passive reporting.
New recombinant shingles vaccine (Shingrix) approved. Much more effective but with stronger side effects — 80%+ report injection site reactions. Generated significant VAERS reports.
Explore related data →Pfizer and Moderna mRNA vaccines received Emergency Use Authorization. The largest vaccination campaign in history began, with unprecedented VAERS reporting to follow.
Explore related data →VAERS and v-safe detected myocarditis/pericarditis signal in young males after mRNA COVID vaccines. Risk confirmed at ~1 in 5,000-10,000 for males 16-24 after dose 2.
Explore related data →CDC/FDA recommended pausing Johnson & Johnson COVID vaccine after 6 cases of rare blood clotting (TTS) among 6.8 million doses. Pause lifted after 10 days with updated guidance.
768,706 VAERS reports filed in a single year — more than 10x the typical annual volume. Driven by massive COVID vaccination campaign and heightened public awareness.
Explore related data →Johnson & Johnson voluntarily withdrew its COVID vaccine from the U.S. market, citing low demand. The TTS blood clotting risk, though rare, contributed to low uptake.
First RSV vaccines approved for adults 60+. Abrysvo and Arexvy entered the market, adding new data streams to VAERS.
With H5N1 bird flu spreading in dairy cattle and poultry, the U.S. government stockpiled pre-pandemic vaccines and began planning for potential mass vaccination campaigns.
HHS/RFK Jr. administration announced development of AI tools for analyzing VAERS data, signaling renewed government focus on vaccine safety monitoring.
Vaccine safety monitoring has evolved dramatically over 70 years. Today's system — VAERS, VSD, CISA, and v-safe — represents multiple layers of surveillance that didn't exist for most of vaccine history.
Every withdrawal and detected signal on this timeline is evidence that the system works: problems are found and addressed. The challenge is communicating that monitoring process to a public that often hears about risks without the context of how they were detected and resolved.
Several recurring themes emerge from over seven decades of vaccine safety history:
As of mid-2026, vaccine safety monitoring sits at an inflection point. The HHS administration under RFK Jr. has signaled increased scrutiny of vaccine safety data, including the development of AI-powered tools for analyzing VAERS reports. Whether this leads to more sophisticated signal detection or politicized data interpretation remains to be seen.
Meanwhile, the post-pandemic normalization of VAERS reporting continues. Annual reports are returning to the 35,000-45,000 range typical of the 2015-2019 era, while new vaccine entries like RSV immunizations add fresh data streams to monitor. The potential for H5N1 avian flu vaccination campaigns adds another variable that could reshape the reporting landscape if a pandemic emerges.
The fundamental challenge remains unchanged: balancing the public's right to transparent safety data with the need for responsible interpretation of that data. VAERS was built as an early warning system, not a scorecard — and communicating that distinction remains as important in 2026 as it was in 1990.
VAERS (Vaccine Adverse Event Reporting System) was created in 1990 as a joint program of the CDC and FDA. It is a passive surveillance system that accepts reports of adverse events following vaccination from anyone — healthcare providers, patients, and manufacturers. As of 2026, VAERS contains over 1.98 million reports.
The Cutter Incident of 1955 was one of the worst pharmaceutical disasters in U.S. history. Cutter Laboratories produced improperly inactivated polio vaccine that contained live poliovirus, causing approximately 40,000 polio cases, 200 cases of paralysis, and 10 deaths. It led to much stricter vaccine manufacturing oversight and is considered a turning point in vaccine safety regulation.
COVID-19 vaccines caused an unprecedented surge in VAERS reporting. In 2021 alone, 768,706 reports were filed — more than 10 times the typical annual volume. This was driven by the largest vaccination campaign in U.S. history (670+ million doses administered), heightened public awareness, and mandatory reporting requirements for healthcare providers administering EUA vaccines.
Yes, VAERS played a critical role in detecting the myocarditis safety signal associated with mRNA COVID-19 vaccines in 2021. The system flagged an unusual number of myocarditis reports in young males after the second dose. The signal was then confirmed through more rigorous studies, and the FDA added warning labels to the Pfizer and Moderna vaccines.
The Johnson & Johnson (Janssen) COVID-19 vaccine was paused in April 2021 after 6 cases of rare blood clotting (thrombosis with thrombocytopenia syndrome, or TTS) were detected among 6.8 million doses. The pause was lifted after 10 days with updated guidance. J&J ultimately withdrew the vaccine from the U.S. market in 2023 due to low demand.
The U.S. vaccine safety monitoring system in 2026 is a multi-layered infrastructure built from the lessons of the events described above. Understanding each layer helps put VAERS data in context:
Together, these systems create overlapping layers of safety monitoring. No single system is perfect, but they complement each other. VAERS serves as the front door — the widest net — while VSD, CISA, and BEST provide the rigorous analysis needed to determine whether a signal represents a real risk.
Several concepts are essential for understanding the events on this timeline:
This timeline covers major events in U.S. vaccine safety history. It is not exhaustive — many smaller but important developments in vaccine manufacturing, regulation, and surveillance are not included. The events selected represent turning points that shaped today's safety infrastructure.
All data referenced on this page comes from official VAERS public-use datasets published by the CDC/FDA, peer-reviewed medical literature, and government reports. For our complete data methodology, see the methodology page.