Polio outbreak– The Philippines

On 27 September 2019 , a circulating vaccine-derived poliovirus type 1 (cVDPV1) has been confirmed in environmental samples in Philippines. The virus has been isolated from ten environmental samples, all genetically related, which were collected from one sewage collection site and its tributary pumping stations in Manila, between 1 July and 23 September 2019. This sewage collection site in the city of Manila has a catchment area of over 600,000 people.

Vaccine-derived polioviruses are rarely occurring forms of the poliovirus that have genetically changed from the attenuated (weakened) virus contained in oral polio vaccine. They only occur when the vaccine virus is allowed to pass from person to person for a long time, which can only happen in places with limited immunization coverage and inadequate sanitation and hygiene. Over time, as it is passed between more unimmunized people, it can regain the ability to cause disease. When the population is fully immunized with both oral polio vaccine and inactivated polio vaccine, this kind of transmission cannot take place. The gut immunity in people immunized with oral polio vaccine stops the virus from being passed on. Full immunization therefore protects against both vaccine-derived and wild polio viruses.

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