Table 2. Reported incidents of poliovirus release from laboratories and vaccine production facilities in the post–polio vaccine era*.

Year	Location (reference)	Source	Poliovirus type	No. cases	Exposure			Description
					Primary	Secondary	Tertiary
1955	United States (27,28)	Vaccine production facility	Not indicated	164	Vaccine recipients(≈40,000 children)	113 contacts of the children	NA	“Cutter incident”; inadequate formaldehyde virus inactivation during poliovirus vaccine production (≈120,000 doses); ≈40,000 children experienced muscle weakness, of whom 51 experienced paralysis; 5 deaths; 113 contacts of the children were also paralyzed, of whom 5 died
1991	France (29)	Lab and vaccine production facility	WPV3 (Saukett) strain	1	No definitive information on exposure of case			Saukett strain isolated in France from a woman from Algeria; source of this lab strain could not be confirmed
1992	Netherlands (30)	Vaccine production facility	WPV1 (Mahoney) strain	1	Father (worker at facility)	Son	NA	Boy (age 19 mo) with respiratory symptoms (no paralysis); father with history of accidental exposure to Mahoney strains while working in a poliovirus vaccine production facility
1993	Netherlands (30)	Vaccine production facility	WPV3 (Saukett) strain	1	No definitive information on exposure of case			Child with gastroenteritis (no paralysis); had travel history to France; no epidemiology established to trace lab exposure; Saukett strains typical for IPV production in France isolated from the stool samples
2000	India (31–33)	Lab and vaccine production facility	WPV2 (MEF-1) strain	3	No definitive information on exposure of case			WPV2 isolates found in Sep 2000 and Nov 2002–Feb 2003 from 10 children with AFP, 1 healthy contact, and 1 environmental sample; isolates unrelated to all previous WPV2 strains found in India; because this was a lab reference strain and not a community-derived wild strain, lab source was suspected
2002–2003	India (31–33)	Lab and vaccine production facility	WPV2 (MEF-1) strain	8	No definitive information on exposure of case
2014	Belgium (34,35)	Vaccine production facility	WPV3 (Saukett) strain	0	NA	NA	NA	≈1013 infectious WPV3 particles accidentally released into sewage system from production plant in Belgium; no poliovirus detected in environmental or human samples
2017	Netherlands (12)	Vaccine production facility	WPV2 (MEF-1) strain	1	Worker	None	None	Accidental leakage in vaccine production room; 1 of 2 exposed staff members tested positive by RT-PCR

*Cases are defined as laboratory positive (with or without paralysis) for poliovirus by standard methods of virus isolation or known exposure to poliovirus. AFP, acute flaccid paralysis; IPV, inactivated poliovirus vaccine; lab, laboratory; MEF-1, wild poliovirus type 2 laboratory reference strain; NA, not applicable; RT-PCR, reverse transcription PCR; WPV, wild poliovirus; WPV1, wild poliovirus type 1; WPV2, wild poliovirus type 2; WPV3, wild poliovirus type 3.