Polio vaccine: understand the risks of not immunizing children against the disease

This Monday (08/08) began the national vaccination campaign against poliomyelitis, a disease with serious consequences considered eradicated in Brazil since 1989, but with a risk of the emergence of new cases due to low vaccination adherence.

Children under five years of age can be vaccinated and, in parallel, children under 15 also have the chance to update their vaccination booklet. Immunizations are made free of charge by the SUS (Unified Health System) and take place until September 9.

The recommended vaccination coverage range for poliomyelitis, according to Fiocruz, is 80%. In 2021, polio immunization was only 67.1%.

“One of the likely reasons for this vaccine drop is the false sense of protection from diseases they don’t know about. Polio, along with measles, was once one of the main childhood diseases in terms of sequelae and deaths, but today’s parents and guardians nowadays they belong to a generation that was very vaccinated, and therefore, they have no experience with the disease”, points out Juarez Cunha, president of SBIm (Brazilian Society of Immunizations).

What can happen to those who are not vaccinated against polio

Poliomyelitis is an infectious disease caused by a virus that lives in the intestine, called poliovirus (existing in serotypes 1, 2 and 3). The agent is able to infect children and adults through direct contact with feces or secretions passed through the mouth of infected people.

When it comes to a person without a history of vaccination, that is, without immune protection against the poliovirus, after an infection, the agent begins to multiply freely in the throat or intestines.

Then the virus reaches the bloodstream and, if the condition is not treated in time, it can reach the brain, causing the so-called “paralytic infection”.

In these rarer cases, but which can cause irreversible sequelae, the virus attacks the nervous system, destroying motor neurons and causing paralysis in the lower limbs.

That’s what happened to the famous Mexican artist Frida Kahlo, who had polio at the age of six and ended up with permanent damage to her leg movements. Later, due to complications from the disease, the painter still had to amputate her toes and, later, one of her legs.

Another possibility is that the virus, after reaching the brain, causes meningitis, inflammation of the membranes that cover the brain and spinal cord, whose main symptoms are fever, stiff neck and nausea.

If not treated properly, meningitis can also cause sequelae. These include partial or total loss of hearing and vision, epilepsy and paralysis on one or both sides of the body.

If the cells of the nerve centers that control the respiratory and swallowing muscles are infected, the disease can affect the person’s ability to breathe normally and eat, which can lead to death.

“The consequences of the disease were very important and impacted the lives of many Brazilians in the past, since practically everyone had someone in the family who suffered from the disease or at least knew someone who was infected before the eradication of the disease”, indicates the president. from SBIM.

Why can polio come back if the disease was already eradicated?

Brazil is one of eight South American countries that are at high risk of a return of polio, according to a report released by PAHO (Pan American Health Organization) in 2021.

Today, the disease only exists in an endemic form (circulating year-round), in Afghanistan and Pakistan in neighboring countries in South Asia.

But poliomyelitis has appeared in the form of a “vaccine derivative” in the United States, Israel, England and other countries, which raises a warning for the whole world.

Viruses that circulate from a modified form of the virus originally contained in OPV (the oral polio vaccine) are called “vaccine derivatives”.

As Juarez Cunha explains, when a child receives the oral vaccine (used in Brazil only for booster doses), which uses the attenuated virus (alive, but weakened), part of this virus can come out in the feces and end up in the sewer, as was observed in London last June, increasing the risk of infection for those who have not been vaccinated.

According to a document from the “Polio Global Eradication Initiative”, a WHO initiative to eradicate the disease, on rare occasions, when replicating in the human intestine, OPV strains undergo genetic mutations and can spread in communities that do not are fully vaccinated against polio, especially in areas where there is poor hygiene, where sanitation is poor or where there is overcrowding.

“Other mutations occur as these viruses spread from person to person, and if one of them manages to continue to spread in an undervaccinated population, it could, over time, mutate genetically to the point where it regains the ability to cause paralysis.” , says the document.

Experience shows that low polio vaccine coverage is the main risk factor for the emergence and spread of a vaccine-derived outbreak.

If the oral vaccine is given to only a few people in a large susceptible population, the vaccine virus can continue to multiply, change genetically, and infect unvaccinated people. A population that has been extensively vaccinated will be protected against mutation and spread of the virus.

“For this, vaccination coverage needs to be better in many countries, including Brazil, which before 2015 was considered an example to be followed in terms of immunization against polio”, points out Gislayne Castro e Souza de Nieto, pediatrician and neonatologist and professor of the Medicine course at Universidade Positivo, in Curitiba, Paraná.

Both experts consulted by BBC News Brasil point out that, in the future, the tendency is for only inactivated virus vaccines to be used – in Brazil and in all other countries.

But this is a change that must happen gradually, and until it is completed, all places where there is low vaccination coverage are at risk. “In the US, only the immunizing agent with inactivated virus is used, but even so, a case of infection by a derivative of the vaccine was reported. It probably happened by someone who traveled”, points out Cunha.

In addition to the need for high vaccination coverage, another important point in combating new outbreaks is surveillance of “flaccid paralysis”, as cases of loss of movement caused by polio are called. “It is important to check if they are motivated by the disease, but this is a surveillance that we are not able to do in Brazil”, he indicates.

Finally, the lack of active environmental surveillance that constantly checks for polioviruses circulating in sewage also contributes to making Brazil more susceptible to new cases.

How to get the vaccine against polio and other diseases

Vaccination is the only way to prevent polio. In order for the child to receive the immunization agent, it is sufficient for his/her legal guardian to take him/her to a vaccination post.

The national polio campaign seeks to reach children under five years of age who have not yet been vaccinated with the first doses of the immunizer (which is given at 2, 4 and 6 months of age by intramuscular injection) or who have not yet taken the doses booster with the bivalent oral vaccine – OPV (droplet).

For adolescents under 15 years of age, the immunizers available at vaccination centers are against hepatitis, pneumonia, rotavirus, yellow fever, measles, mumps, rubella, chickenpox, HPV, diphtheria, meningitis, among others.

– This text was published in https://www.bbc.com/portuguese/brasil-62471680