After exploring smallpox eradication in our last article we look at what we hoped would be our next success: Polio.
Poliomyelitis, caused by the poliovirus, is an old disease for the human race. Evidence of epidemics predate history – in fact, there is possible evidence that polio was causing disease in ancient Egypt. The first clinical description of people occurred in 1789 by a British doctor called Michael Underwood. It has spread across the world to cause disease and disability to millions but has since been beaten back to three endemic countries: Pakistan, Afghanistan, and Nigeria.
Poliovirus is a picornavirus (a family that also includes multiple disease causing pathogens including rhinovirus – the common cold) which is transmitted through the oral-faecal route. It causes a wide range of disease including asymptommatic all the way to meningitic acute infection. The most well-known sequelae of polio infection is residual disability from the paralytic illness due to destruction of motor neurons. Polio was a global health issue since it was discovered with infections across the entire world with epidemics common. One large epidemic in New York in 1916 saw 9000 cases with 2,343 deaths.
As such, vaccination with a view to control the spread was a goal. Two early attempts at this were made by Maurice Brodie and John Kolmer in 1935, both in the United States. Brodie’s vaccine was made from a killed virus and did not produce enough of an immune response to confer protection – although it did have an issue with severe allergic response. Kolmer’s vaccine from a live virus had the opposite issue with it not being attenuated enough and causing cases of polio. Neither of these vaccines were tested on animals extensively enough before moving on to (at the time) unregulated human trials. These ended poorly and the vaccine roll-out was ended early. One benefit is that this led to increased public scrutiny of future trials.
The first successful vaccine was developed by Jonas Salk in 1952. His vaccine was a killed-virus like Brodie’s produced by culturing polio virus in monkey cells before killing them with formaldehyde. He found that introducing this as a vaccine provoked a strong antibody reaction leading to immunity. Field trials involving 2 million children were performed in 1954 and the vaccine became more widely distributed. In 1955-1957 the incidence of polio in the United States dropped by 85-90%.
In 1962, a different researcher called Albert Sabin developed his own vaccine. This was an oral vaccine made from attenuated live virus which provided comparable efficacy and safety to the Salk vaccine but was easier to administer. This was adopted in the majority of the Western world and contributed to the elimination of polio from the United Kingdom, Australia, the United States, and much of Europe by 1988. This suggested that not only could polio be prevented, it could also be eliminated.
Spurred by the success that had already occurred in the developed world, the WHO started the Global Polio Eradication Initiative in 1988 aiming to eradicate it from the 125 countries where it remained endemic. They set a deadline of 2000 for this eradication to occur. By the time 2000 had hit polio cases were down to 719 cases world wide, a 99% reduction. As it stands, three nations continue to have wild and vaccine-derived poliovirus transmission with a further five having only vaccine-derived transmission.
A big part of this is the transmissible nature of the polio vaccine. As it is an attenuated but live virus, it can be transmitted from child to child spreading immunity. However, as the virus mutates it can eventually develop into a form which can cause polio disease. These are called vaccine-derived polioviruses. The concern around this has led the United States to swap back to the Salk vaccine in 1997. However, following a review of the data, the WHO has decided to stick to the oral polio virus due to its important role in eradication. Vaccine-derived polio occurs in the Democratic Republic of Congo, Niger, Papua New Guinea, Somalia, and the Syrian Arab Republic – these nations are not considered endemic as there is no circulating wild poliovirus.
Currently, only three nations continue to have wild poliovirus – Afghanistan, Pakistan, and Nigeria. All three of these nations are limited by difficult healthcare infrastructure, limited access, and recent political instability. Pakistan additionally has seen an increase in attacks against vaccination campaigns. The cause behind this is due to the rise in fake news with the vaccination campaign being accused of acting as a western plot to sterilize the population. Similar conspiracy theories such as these are common and have grown since the discovery that the CIA did use a fake vaccination campaign to track down Osama Bin Laden.
However, these are being tackled by using local representatives and experts in each nation. Nigeria in particular has used local religious leaders to advocate for the benefits of vaccination. This strategy, along with routine immunisation, vaccination days, and specific efforts to access hard to reach populations are driving forward the vaccination campaign. The main threats currently are (as always) fake news, and a sense of inertia close to the finish line. If the campaign continues to push forward, we will likely celebrate a second successful eradication of a human disease in our lifetime.
Author Details: Dr. Eliot Hurn, Foundation Year 2 County Durham and Darlington Foundation Trust.