The stories about this introduced me to the concept of a vaccine-derived polio. Basically, the weakened form of polio that is in the vaccine, which usually sur

The stories about this introduced me to the concept of a vaccine-derived polio. Basically, the weakened form of polio that is in the vaccine, which usually survives in your GI tract for a couple weeks before being eliminated, can be passed onto others if there is a lack of basic sanitation (polio is primarily transmitted through infected fecal matter). If this is in a community with low immunization rates, the vaccine-derived virus can survive much longer than intended. This can actually provide a benefit to others, because they will achieve some level of immunity from the weakened virus. However, if the weakened virus is allowed to circulate for a long time (>1 year), it has the (unlikely) chance to mutate and become less weak. Of course, the number of severe polio cases that have been avoided by the vaccine vastly outweighs the number of vaccine-derived cases. But I thought this was an interesting concept! > ...more than 13 million cases of polio have been prevented, and the disease has been reduced by more than 99%. During that time, 24 cVDPV (circulating vaccine-derived polio virus) outbreaks occurred in 21 countries, resulting in fewer than 760 VDPV cases. More here: https://www.who.int/westernpacific/news/q-a-detail/what-is-vaccine-derived-polio https://www.who.int/westernpacific/news/q-a-detail/what-is-v...