The European Centre for Disease Prevention and Control announced that on Sept. 2, about 45 liters of concentrated live poliovirus was “released into the environment” as a result of human error at a GlaxoSmithKline facility in Rixensart, Belgium.

The ECDC reported that the liquid had been treated at the Rosieres water treatment plant before being released into the Lasne River, which joins the Scheldt River (known as the Escault River in France). Belgium’s Scientific Institute of Public Health confirmed that the liquid was not returned to the drinking water supply chain.

A risk assessment by Belgium’s High Council of Public Health concluded that the risk for infection is low due to high dilution and the high rate of vaccination in Belgium (95%). However, the ECDC reported that susceptible populations living downstream near the Scheldt River in the Netherlands may be at risk if exposed to contaminated water or mud.