The world will be declared polio-free when all regions have documented the absence of wild poliovirus transmission for at least three consecutive years and laboratories holding wild poliovirus materials have adopted appropriate measures for containment. The probability of wild poliovirus transmission from the laboratory to the community is small but the potential consequences of such transmission become more serious as polio-free countries increase in number and immunization decreases or stops. It is crucial to achieve the safe handling, and ultimately, the appropriate laboratory containment, of wild poliovirus infectious materials, as well as potential wild poliovirus infectious materials.
The first edition of the global action plan for laboratory containment of wild polioviruses was issued by WHO in December 1999. It was based on broad input from biosafety experts, epidemiologists, laboratory scientists, ministries of health and vaccine manufacturers.
WHO Global Action Plan for poliovirus containment
More information is here.