Poliomyelitis cases derived from the vaccine

The mbadive vaccination campaign conducted over the past 30 years has almost completely eliminated polio, a condition that has conditioned the existence of humanity for millennia with major epidemics affecting mainly children and leading to permanent forms of paralysis. Vaccines have been essential to achieve this result, but in some countries the inability to provide adequate coverage of the population has led to rare cases of poliomyelitis resulting precisely from vaccination. It is a disease that occurs in a very small number of patients, as we will see precisely because of the insufficient number of vaccinated in some parts of the world, but it is more and more frequent, especially from the latest data published by international health authorities.

In 2017, the polio cases resulting from the vaccine exceeded for the first time those due to the wild version of the virus. The year 2018 ends with similar results: 98 confirmed cases of poliomyelitis vaccine against 29 cases due to the wild version of the virus. The data should not be underestimated and show that there is still work to be done to eradicate the disease, taking into account the health policies adopted so far.

In the richest countries, poliomyelitis vaccine is given by injection. The preparation contains inactivated viruses that cause the disease and induce the creation of antibodies in the blood: if you drink contaminated water containing the virus in its wild form, you are protected from the disease because your own Immune system learned to recognize it. and fight him before he can do any damage. However, the virus remains alive in the intestine for a few weeks, where it multiplies and is expelled into the feces, which can contaminate other unvaccinated people.

Things get even more complicated if you use the other form of vaccine, which contains live virus in an attenuated form and is administered orally. This system is much cheaper than the previous one, it does not require the presence of medical personnel to perform injections, and has therefore found great utility in the poorest countries and developing countries. Who receives the dose, releases with feces the attenuated version of the virus for a few weeks, with the risk that it comes into contact with other people, for example by contaminated water due to poor hygiene conditions.

In this case, a kind of virtuous circle begins: the virus is however harmless and will allow other people to be vaccinated. This process has played an important role in reducing polio cases in the poorest countries in recent decades, but has some negative effects. The more the attenuated virus remains in circulation, the more it increases the risk that it will switch to mutations until it takes a form similar to that of the current wild virus, which causes severe forms of paralysis. .

Wild poliovirus type 2, one of three viral strains, is the one that most easily follows this process: it is estimated that it is causing 90% of cases of paralysis of the Poliomyelitis resulting from the mutation of an attenuated virus used in oral form of the vaccine. In 2015, type 2 was officially declared eradicated, which led the next year to the choice of reviewing the formulation of the vaccine generally administered, leaving only the two strains to be eradicated. Substitution, coordinated by the United Nations, involved more than 150 countries and was accompanied by the adoption of a second injection vaccine, specifically designed to stop the circulation of mutations in the attenuated vaccine.

However, the injections are more expensive and require the presence of medical personnel, a situation that has led to serious gaps in immunization coverage in the most vulnerable countries, such as the Democratic Republic of Congo, Niger, Somalia and Nigeria. . In these and other countries, type 2 mutations have continued to circulate, resulting in an increase in the number of polio cases derived from the oral vaccine. Sample badyzes in these African countries have also highlighted the ability of the virus to spread rapidly, another area of ​​concern for health authorities.

New polio cases due to mutated virus mutations are still quite rare, but they are not good news for Africa anyway. The last person paralyzed by the wild polio virus was reported in Nigeria in 2016, so the disease was probably eradicated on the continent.

Vaccines have been essential in almost completely eliminating one of the most dangerous and disabling childhood diseases, such as polio, which has saved millions of people around the world. The wild version of the virus has been almost completely destroyed, except in Afghanistan and Pakistan, where problems remain due to deficiencies in immunization systems. Eradicating a disease on such a large scale is not easy and involves unexpected events, as evidenced by the history of the oral vaccine, which will require the use of the vaccine to inject to reduce the circulation of mutated versions of the virus. As with smallpox, the eradication of poliomyelitis remains one of the most important health outcomes in the history of mankind, thanks to vaccines.