In April 1955, just weeks after the polio vaccine was licensed in the United States, some children who received their shots fell ill with the very disease the vaccine was designed to prevent. Investigators soon traced the cases to doses made by Cutter Laboratories, which contained live poliovirus instead of inactivated virus. The Cutter Incident involved a faulty batch of the Inactivated Poliovirus Vaccine (IPV), which normally uses killed virus particles to trigger immunity without risk of disease. Unlike the later Oral Polio Vaccine (OPV), which contains weakened live virus and is given by mouth, IPV is delivered by injection and is safer because it cannot revert to an infectious form. The episode, later called the Cutter Incident polio vaccine crisis, left thousands affected and permanently changed vaccine safety oversight. [1]
Polio was one of the most dreaded illnesses of the early 20th century. Each summer, outbreaks left children paralyzed or dependent on iron lungs to breathe. The arrival of Jonas Salk’s inactivated polio vaccine in 1955 was hailed as a breakthrough. The vaccine used a “killed” version of the virus to trigger immunity without causing disease. After successful trials, the government moved quickly to make the vaccine widely available.[2]
To meet urgent demand, multiple companies, including Cutter Laboratories of California, were licensed to manufacture the vaccine.
Not long after vaccinations began, doctors noticed children developing polio within days of receiving their shots. Investigations revealed that some Cutter vaccine lots had not been fully inactivated. Instead of a harmless killed virus, those doses contained live poliovirus capable of causing infection.[2]
The impact was immediate and devastating:
About 120,000 doses were distributed before detection.
About 40,000 children developed polio.
200 cases of paralytic polio were recorded directly in vaccine recipients, with ten deaths.[2]
The U.S. Surgeon General quickly suspended the vaccination program and recalled Cutter’s products. Epidemiologists traced the cases back to specific lots, confirming the source. While production problems were identified at Cutter, the event revealed weaknesses in oversight at the national level, including the testing and approval process for vaccine batches.[1]
The Cutter Incident forced the government to strengthen rules for vaccine manufacturing and monitoring. New standards for testing, tighter federal inspections, and clearer accountability systems were introduced to ensure such a failure would not happen again. Vaccination campaigns resumed later in 1955, this time under much stricter safety conditions.[2]
The Cutter Incident remains one of the most important lessons in vaccine history. What was meant to be a life-saving intervention instead harmed children and families, but the tragedy also reshaped how vaccines are regulated. The stricter safety measures implemented after 1955 continue to guide vaccine development and oversight today, ensuring that public health protection remains the priority.[3]
References:
Centers for Disease Control and Prevention (CDC). 2023. “Historical Vaccine Safety Concerns.” Last modified December 7, 2023. https://www.cdc.gov/vaccine-safety/historical-concerns/index.html.
U.S. National Library of Medicine. 2006. “The Cutter Incident: Poliomyelitis Following Formaldehyde-Inactivated Poliovirus Vaccination in the United States.” PubMed Central (PMC). Accessed October 1, 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC1383764/.
Covington, Nate. 2021. “The Tainted Polio Vaccine That Sickened and Fatally Paralyzed Children in 1955.” NateCovington.com. Accessed October 1, 2025. https://www.natecovington.com/health/the-tainted-polio-vaccine-that-sickened-and-fatally-paralyzed-children-in-1955.
World Health Organization (WHO). 2023. “Poliomyelitis.” Updated October 24, 2023. https://www.who.int/news-room/fact-sheets/detail/poliomyelitis.
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