The two vaccines that brought us to the brink of eradicating polio | Explained Premium

Polio eradication is one of the top priorities of the World Health Organisation (WHO). Since Africa was declared polio-free in August 2020, the wild poliovirus has been restricted to rural pockets in Afghanistan and Pakistan. But from here, the virus is beginning to reappear in big cities in these two countries, which means we won’t eradicate polio this year either.

In 1948, microbiologists John F. Enders, Thomas Weller, and Frederick Robbins were trying to find a method to grow different viruses in cell cultures. In a routine experiment involving human muscle and skin cells, they decided to test one more virus along with the ones they were already testing, since a vial containing that virus was in their freezer. To their surprise, the virus proliferated and grew well with their method. Their work eventually solved one of the most important scientific problems of the time.

They had just managed to find a way to grow the poliovirus in non-nerve cells.

In the mid-20th century, researchers widely believed the poliovirus could only be grown in cultures of nerve cells. This misconception was propagated by their inability to infect rhesus macaques by the oral route, and only by directly injecting the virus into the nervous system. At the time, they didn’t know the problem was with the poliovirus strains they were using.

The poliovirus has only one natural host — humans — and many of the early strains of the virus were isolated from humans and wouldn’t infect non-human primates. Since scientists kept passing the virus through the brain tissues of macaques, it adapted to that mode of infection.

The inability to culture polio in non-nerve cells was a major roadblock to developing a polio vaccine. But thanks to Enders and his team, the poliovirus could now be mass-produced for vaccine research.

Polio eradication is one of the top priorities of the World Health Organisation (WHO). Since Africa was declared polio-free in August 2020, the wild poliovirus has been restricted to rural pockets in Afghanistan and Pakistan. But from here, according to a recent report in Science, the virus is beginning to reappear in big cities in these two countries.

This reemergence is a result of vaccine hesitancy due to misinformation, conflict, poverty, and limited access to these isolated regions. The WHO’s Global Polio Eradication Initiative is thus set to miss its deadline of eradicating polio by the end of 2024.