It seems like a good time for a bit of good news – after two decades of concerted effort, wild-type polio has been eliminated entirely from Africa. There are now only two countries in the world with endemic wild polio, Pakistan and Afghanistan. Once again, we are on the brink of worldwide polio eradication. The world needs to come together for one final push to eradicate this disease forever.
I say “once again” because we were here 20 years ago, but missed our chance. In 2002 the World Health Organization predicted they could eliminate polio from the last African country, Nigeria, by the end of the year. Then, by 2005, they hoped to eradicate polio from the last countries on Earth, India, Pakistan, and Afghanistan. Those hopes were dashed, however, by anti-vaccine rumors spreading in Nigeria.
Specifically some Muslim clerics were concerned that the vaccine program was entirely introduced by Westerners whom they did not trust. They spread fears that the vaccine either contained the AIDS virus as a campaign of deliberate infection, or sterilizing agents so that Muslim women could not have children. This led to decreased vaccine compliance, and polio cases in Nigeria skyrocketed from single-digits to over a thousand, eventually spreading to other African nations. It has taken almost two decades to crawl back to where we were in 2002, and now the WHO’s efforts have succeeded in achieving zero cases of wild-type polio in Africa.
Polio is caused by a virus that infects motor neurons in the spinal cord. When these nervous cells die, this breaks the connection between the brain and the muscles those cells connected to. Further, these motor neurons keep muscle cells alive and healthy, so once the neuron dies, then the muscle cells they were previously connected to atrophy and eventually die also. The result is muscle wasting and weakness.
There are three strains of wild-type poliovirus. Two of these strains have already been eradicated from the world, but one remains. There is also vaccine-derived polio (see this discussion of the two types of vaccines). In rare cases the live virus vaccine can spontaneously mutate back to a more infectious type, and cause an actual polio infection. This vaccine-derived virus can then spread to those who are not protected by vaccination.
This happens when the live attenuated virus from the vaccine is excreted by the person vaccinated and gets into the local water supply. There it can spread to others in the community. This is actually mostly a good thing, because it can produce immunity in those who are exposed. The vaccine also protects against this vaccine-derived virus, and so the spread is limited in a vaccinated population. If, however, there are large numbers of unvaccinated people, the vaccine-derived virus can last for longer in the environment. This gives the virus more time to mutate, and on very rare occasions can mutate back to a form that can produce paralysis. If a community is fully vaccinated, however, this won’t happen.
To put this into perspective, the WHO estimates that the polio vaccine program in Africa over the last 20 years prevented millions of cases of wild-type polio, but caused hundreds of cases of vaccine-derived polio – about 10,000 cases prevented for every one case produced. Further, newer versions of the vaccine, which do not include the wild-type-2 strain of the virus which has been eradicated, produce much fewer cases of vaccine-derived paralysis.
The bottom line is that a thorough vaccine campaign prevents both wild-type polio and, ironically, vaccine-derived polio (by reducing the duration of spread in the environment and therefore opportunity to mutate).
It should also be emphasized that it is possible to fully eradicate polio. The virus has no non-human host, no reservoir in which it can survive and re-infect people. So if we reduce human cases to zero – the virus is gone. Just as with smallpox, it can be completely eradicated. But this is an all-or-nothing game. Close is not good enough. Polio is a highly contagious virus. If even a single case remains and spreads, we could be seeing hundreds of thousands of cases worldwide within a decade. This means that all countries need to keep up their polio vaccine program until worldwide eradication is achieved.
How close are we? So far in 2020 there have been 37 reported cases (of the wild-type infection) in Afghanistan and 65 cases in Pakistan (and zero in the rest of the world). Those numbers are low, but they can increase rapidly if vaccine efforts are not maintained. There is an aggressive vaccine program in these remaining countries but, as the WHO reports:
Unfortunately, children are still missing out on vaccination for various reasons including lack of infrastructure, remote locations, population movement, conflict and insecurity and resistance to vaccination.
In Afghanistan resistance is coming mainly from the Taliban, but not because they fear the vaccine, they fear Western spies and drone strikes. They have essentially banned door-to-door vaccine efforts in the territories they control. They do allow vaccine clinics, but these are too sparse to reach everyone who needs to be vaccinated. We need to get to 95% coverage to stop spread of the virus. This is a purely political problem, and may be the final stumbling block that prevents worldwide eradication.
There is a lot going on in the world, especially with a pandemic, but the fate of polio should not be overlooked. Eradication is permanent, and failure to eradicate means the entire world is still at risk for renewed polio outbreaks. This issue should be getting far more attention than it’s getting. The entire world has a stake in this, and the attention of the world should be fixed on Pakistan and Afghanistan until we cross the finish line. At this point, any resources spent to achieve this goal are worth it.