Polio vaccines predicted loss of effectiveness

US, WASHINGTON (ORDO NEWS) — Epidemiologists from the World Health Organization (WHO) found that polio vaccines could soon become useless to protect children. The fact is that mutant forms of poliovirus, which are associated with one of the previously developed vaccines, are spreading around the world. The findings of experts published the scientific journal Science.

“Global efforts to eradicate poliomyelitis are in a paradoxical situation. On the one hand, current poliomyelitis outbreaks cannot be controlled without a vaccine based on a weakened poliovirus of the second type. On the other hand, new mutant versions of the virus appear due to these vaccines. The risk of widespread virus circulation is growing because global immunity to it is rapidly declining, “the scientists write.

Poliomyelitis is an acute infectious disease that causes poliovirus. The disease is difficult, its pathogen can be transmitted by airborne droplets and through physical contact. The virus infects the gray matter of the so-called front horns of the spinal cord and other parts of the central nervous system, which leads to partial or complete paralysis.

The most effective way to fight polio is through vaccination. Since the middle of the last century, doctors began to successfully use two types of vaccines: live and deactivated. The first type of vaccine can be either monovalent, based on one attenuated virus, or combined, which combines several strains of polioviruses of different types.

At the turn of the century, as noted by Roland Sutter, coordinator of the polio research program at WHO, and his colleagues, doctors faced a new problem: one of the components of the “live” vaccine, attenuated type 2 polio virus (OPV2), began to mutate and cause outbreaks this disease.

A new polio epidemic

Since by that time the natural reservoir of the second type of virus had already been completely destroyed, WHO specialists and heads of leading medical organizations decided to stop using OPV2 as a component of combined polio vaccines. Sutter and his team specified whether any effect of this measure was manifested.

To do this, scientists collected virus samples that caused polio outbreaks in different countries of the world since April 2016, when doctors began to use vaccines without OPV2. Specialists decoded their genomes and compared them with each other.

Sets of small mutations in the genetic code of the virus showed that measures by WHO and local health organizations as a whole seriously reduced the number of victims of mutant varieties of the vaccine poliovirus of the second type. However, they could not completely suppress its spread.

Moreover, the data collected by scientists indicate that outbreaks of this form of poliomyelitis appear more often. This is due to various factors. First, in those regions where a mutant version of this pathogen is distributed, a monovalent vaccine based on a weakened version of the second type of poliovirus is widely used. Secondly, the total proportion of people who have developed immunity under the influence of an old vaccine is rapidly decreasing.

As a result of attempts to eradicate poliomyelitis, more and more dangerous and infectious mutant forms of a weakened virus appear that affect children and adults with weakened immunity after the previous outbreak of this disease has ended. Therefore, WHO experts urge scientists to develop new vaccines as soon as possible to replace OPV2, which will not lead to the emergence of mutant versions of poliovirus.

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The article is written and prepared by our foreign editors from different countries around the world – material edited and published by Ordo News staff in our US newsroom press.