The polio vaccine: Understanding the risks of not immunizing children

The polio vaccine: Understanding the risks of not immunizing children

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

Children under the age of five can be vaccinated, and in parallel, children under 15 also have the opportunity to update their vaccination booklet. Vaccinations are carried out free of charge by the SUS (Unified Health System) and last until September 9.

  • What is the polio disease known as polio?
  • The government begins a national campaign to vaccinate children and adolescents against polio and other diseases

The recommended polio vaccination coverage range, according to Fucruz, is 80%. In 2021, the polio immunization was only 67.1%.

“One possible reason for this drop in vaccination is a false sense of protection from diseases they know nothing about. Polio, along with measles, was one of the major childhood diseases in terms of consequences and mortality, but today’s parents and guardians nowadays belong to a generation He was heavily vaccinated, and therefore, they have no experience with the disease,” notes Juárez Cunha, president of the SBIm (Brazilian Society for Immunization).

What can happen to people who are not vaccinated against polio

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

When it comes to a person who does not have a history of vaccination, that is, without immune protection against the polio virus, after infection, the agent begins to multiply freely in the throat or intestines.

The virus then reaches the bloodstream, and if the condition is not treated in time, it can reach the brain causing what is called a “paralysis infection”.

In these rare cases, which can cause irreversible sequelae, the virus attacks the nervous system, destroying motor neurons and causing paralysis of the lower extremities.

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

The first doses of the vaccine, together with the inactivated virus, are administered at 2, 4 and 6 months of age by intramuscular injection – Photo: Agência Brasil

Another possibility is that after the virus reaches the brain, it causes meningitis and inflammation of the membranes covering the brain and spinal cord, the main symptoms of which are fever, neck stiffness and nausea.

If meningitis is not treated properly, it can also cause sequelae. These include partial or complete 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 muscles of the respiratory and swallowing system become infected, the disease can affect a person’s ability to breathe normally and eat food, which can lead to death.

“The consequences of the disease were very significant and affected the lives of many Brazilians in the past, where everyone had a family member with the disease or at least knew someone affected before the disease was eradicated,” the president notes. from SBIM.

Why can polio return if the disease has already been eradicated?

Brazil is one of eight countries in South America at high risk of a return of polio, according to a report from the Pan American Health Organization (PAHO) in 2021.

Today, the disease is found only endemic (spread all year round), in Afghanistan and Pakistan in the neighboring countries of South Asia.

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

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

Albert Sabin, the medical researcher who developed the oral polio vaccine, asks five-year-old boy Luis Inacio Gama to open his mouth wide at the Jesus Anti-myelitis Hospital in Rio de Janeiro, in 1967 – Image: Getty Images

As Juarez-Cona explained, when a child receives the oral vaccine (used in Brazil only for booster doses), which uses the attenuated (live but weakened) virus, part of that virus can be excreted in the stool and end up in sewage, as observed in London in Last June, it increases the risk of infection for those who have not been vaccinated.

According to a document from the Global Polio Eradication Initiative, a WHO initiative to eradicate the disease, in rare cases, when reproducing in the human intestine, OPV strains undergo genetic mutations and can spread in communities that are not fully immunized against Polio, especially in areas that lack hygiene, where sanitation is poor or where there is overcrowding.

“Other mutations occur when these viruses spread from person to person, and if one can continue to spread in an immunized population, over time they can mutate genetically to the point where they regain 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 a small number of people in a large susceptible population, the vaccine virus can continue to replicate, change genetically, and infect unvaccinated people. Populations that are widely vaccinated will be protected from mutations and the spread of the virus.

“For this, vaccination coverage should be better in many countries, including Brazil, which before 2015 was considered a role model in terms of polio immunization,” notes Jesline Castro e Souza de Nieto, pediatrician and neonatologist. and Professor of Medicine Course at Positivo University, Curitiba, Parana.

Both experts consulted by BBC News Brasil indicated that the trend in the future is to use only inactivated virus vaccines – in Brazil and all other countries.

But this is a change that has to happen gradually, and while it is not completed, all places with low immunization coverage are at risk. “In the United States, the immunizing agent is only used with the inactivated virus, but nevertheless, a case of infection with a derivative of the vaccine has been reported. It may have occurred by a person who traveled,” notes Cunha.

In addition to the need for high vaccination coverage, another important point in the control of new outbreaks is to monitor “flaccid paralysis”, in which cases of loss of movement due to polio are called. “It is important to check whether the disease is driven by them, but this is a monitoring that we cannot do in Brazil,” he notes.

Finally, the lack of active environmental monitoring that constantly checks for polioviruses circulating in wastewater makes Brazil more vulnerable to new cases.

How to get polio vaccine and other diseases

Vaccination is the only way to prevent polio. In order for the child to receive a vaccination agent, it is enough for his legal guardian to take him to the vaccination center.

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

For adolescents under the age of 15, the vaccinations available at vaccination centers are against hepatitis, pneumonia, rotavirus, yellow fever, measles, mumps, rubella, chickenpox, human papillomavirus, diphtheria, meningitis and others.

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