As a polio survivor myself, I have long been interested in the international campaign to eradicate the disease through vaccinations. Much of the world is now polio-free. But in Pakistan and Afghanistan, last strongholds of wild polio virus, cases increased from 33 in 2018 to 176 in 2019. So far this year, the two countries have confirmed 87 wild polio cases, compared with 64 at this time last year. The real number is likely higher. The vaccination program has been inhibited by Covid-19 precautions and the fears of local populations. Restoration of the Pakistan and Afghanistan vaccination programs will have to overcome the suspicions and refusals that blocked them last year.

Africa is free of the wild virus, but is battling against vaccine-derived virus. So far this year, Africa has reported 133 type 2 cases in 14 countries, up from 47 at this time last year. Hot spots include Ivory Coast and parts of Chad, Mali, Ghana, Togo, Burkina Faso, and Niger.

Oral polio vaccine contains an attenuated vaccine-virus, activating an immune response in the body. When a child is immunized, the weakened vaccine-virus replicates in the intestine for a limited period, thereby developing immunity by building up antibodies. During this time, the vaccine-virus is also excreted. In areas of inadequate sanitation, this excreted vaccine-virus can spread in the immediate community before eventually dying out. This can offer protection to other children through ‘passive’ immunization but may also generate infection with vaccine-derived polio. The risk is small compared with that of having no vaccinations at all, but remains troubling.

Source: Leslie Roberts, “Polio vaccinators are back after pandemic pause,” Science 369, no. 6502 (24 Jul 2020): 360, doi: 10.1126/science.369.6502.360.