How Does The Poliovirus Vaccine Work And What Types Are Available?

Introduction: The Importance of Polio Vaccination

Envision a dystopian world where a life-threatening virus had the power to leave children younger than 5 irreversibly paralysed in a matter of hours, hampering their ability to breathe, walk, run and play… now imagine the devastation of their parents and loved ones upon hearing that the deadly virus affecting their child has no cure once infected. Terrifying, isn't it?

It is harrowing to think that just less than 70 years ago, this was the hideous reality of what once was the most feared disease in the world - Polio or poliomyelitis - a highly contagious viral disease which spread like wildfire. By the mid-20th century, the poliovirus had killed or paralysed over half a million people every year.¹

Today, we live in a nearly polio-free world, thanks to vaccination, which is undoubtedly one of the greatest medical advances in the history of global public health. The polio vaccines have been essential in allowing us to reach this point. Still, continued persistent immunisation is needed to protect future generations to ensure that polio does not return. 

In this blog, we will dive into the what, why and how behind the polio vaccine by exploring the different types of vaccines that have nearly eradicated this terrible disease. 

What is Poliovirus and How Does It Affect the Body?

Polio is caused by the Poliovirus, which enters the body through the nose and mouth; once infected, the virus takes over the nervous system and rapidly destroys the nerve cells that allow us to move our limbs and muscles, resulting in weakness and deterioration followed by paralysis in patients. In more severe cases, the destruction of nerve cells in the part of the brain that controls involuntary actions like breathing, heart rate and blood pressure, the brainstem, can be fatal, in addition, paralysis caused by polio can happen in the lungs and muscles that control your breathing, this can lead to death. For this reason, during the polio outbreaks, the iron lung, which was a medical device created to help polio patients breathe, was utilised. 

Polio is transmitted (spread) from person to person through contact with contaminated water such as open sewage or also via respiratory droplets from an infected person. 

For example, a method that polio can be spread is when non-infected people eat food which is prepared by an infected individual or an uninfected person who may have come into contact with the polio virus and did not wash their hands after using the toilet. After the non-infected person eats the contaminated food, viral particles enter the body through the mouth and then start making more copies of themselves in the intestines, these viral particles are also released into the sewage system after the infected person poops, and the infectious cycle continues.²

Due to the way polio spreads (mostly through contaminated water), it is more common in locations with inadequate sanitation, such as when people defecate outdoors or do not filter water before drinking it.³

Polio mainly affects children under the age of 5, however, anyone who isn't vaccinated can still get the disease. Many infections also show no symptoms, but milder forms of the disease can present with flu-like symptoms such as fever, headache, muscle aches, sore throats, stomach ache, loss of appetite, nausea and vomiting and severe cases can result in lifelong disabilities or death.⁴

Those that survive the poliovirus infection may not recover completely and later in life may develop a condition called post-polio syndrome which occurs many years after being declared as recovered from polio. 

Vaccination is the only way to prevent polio from occurring, and in this disease, prevention is the cure. 

How Do Poliovirus Vaccines Work?

Vaccines train the body’s immune system to fight off harmful pathogens, which essentially are the germs that cause disease in the body, these include viruses and bacteria. The concept of vaccines is rather similar regardless of the disease in question. Vaccines deliver a safe strain of the pathogen into the body; this enables the body to become accustomed to it and begin developing defences against it without actually causing the illness. The body makes chemicals called antibodies which are proteins that identify specific pathogens and selectively kill them before they cause damage. In this way, the body is prepared for the real illness and the immune system is quickly activated and prepares to attack the pathogen faster. This means that vaccination makes sure that the real attack or infection is milder or prevents the body from getting sick enough to present the signs of infection in the first place.⁵ 

The polio vaccines work in the same ways, a weak or dead form of the poliovirus is injected or introduced into the body, and this causes the immune system to create antibodies specific to the poliovirus to attack and neutralise the poliovirus if a person is exposed to it. The polio vaccine does not cause polio but instead primes the immune system to respond faster and more effectively. 

There are two forms of polio vaccines: inactivated poliovirus vaccine (IPV) and oral poliovirus vaccine (OPV). Both are extremely effective, although they work in slightly different ways and are utilised in distinct circumstances.⁶

Types of Poliovirus Vaccines

Inactivated Poliovirus Vaccine (IPV)

The IPV vaccine contains an inactivated or dead form of the poliovirus, which is unable to cause polio in the recipient. The IPV vaccine is given as an injection in the arm or leg. When administered, the IPV vaccine boosts the body to produce antibodies against the killed or inactivated virus, this helps the body to fight off real infection if the situation arises. In case of an actual viral infection of polio, the IPV vaccine attacks the virus in the bloodstream itself with the antibodies produced after giving the vaccine and thus prevents the virus from reaching the nervous system. Therefore, since antibodies are already present, the body can respond to the infection quickly and typically without causing disease in the person at all. 

Moreover, since the IPV vaccine uses an inactivated or dead form of the virus, this vaccine is suitable for those with weaker immune systems. 

The IPV vaccine protects individuals from poliovirus but it cannot stop the spread of the virus, which is why it is important for everyone to be vaccinated in order to eradicate poliovirus. 

Oral Poliovirus Vaccine (OPV)

The OPV contains a live-attenuated form of the polio virus, meaning it is a live and weakened form of the poliovirus. This vaccination is delivered orally, usually as a couple of drops in the mouth. When it is inside the body, the OPV also produces antibodies against the poliovirus.⁶ 

In addition to this, the OPV triggers a strong immunological reaction in the intestines which prevents the weakened virus from making more copies of itself, this means that the spread of polio can be contained as spreading to others through fecal contamination is reduced.⁶ 

OPV is more affordable and easy to administer, making it ideal for mass vaccination programs as the OPV not only protects individuals but also contributes to community immunity, especially in low-resource settings.⁷

Both vaccines are highly effective but are used in different contexts based on the specific needs of a country or region. High-income, polio-free countries primarily use IPV due to its safety profile, as the IPV vaccine produces a weaker immune response than the OPV vaccine, however, OPV is still crucial in areas where polio transmission persists.

Global Efforts in Polio Vaccination

There has been immense progress made since the launch of the Global Polio Eradication Initiative in 1988 when polio was present in 125 countries and paralyzed 1,000 children daily. Immunization efforts and the rollout of the life-saving polio vaccine have reduced polio cases worldwide by more than 99%.⁸

Although the world now is at the cusp of achieving total eradication of the poliovirus globally, the job isn't finished until every country is polio-free. There is still an ongoing risk of outbreaks in areas like Afghanistan and Pakistan where the spread of wild poliovirus still exists. Diligent vaccination is therefore essential to keep the world polio-free.⁹

Strategies to eradicate polio represent globally coordinated efforts by organizations like the WHO, Bill & Melinda Gates Foundation and UNICEF. For instance, the Polio Eradication Strategy 2022-2026 outlines the pathway to achieving a polio-free world by emphasizing stronger immunization campaigns, improved outbreak response, and integration of health services to reach rural populations. The plan also aims to strengthen surveillance, ensure political commitment, and increase accountability to make polio eradication sustainable and irreversible.¹⁰

Summary

• Polio is a highly contagious virus that can cause paralysis and death, but it is preventable through vaccines
• Two types of polio vaccines exist: Inactivated Poliovirus Vaccine (IPV) and Oral Poliovirus Vaccine (OPV)
• Vaccines train the immune system to recognize and fight the virus, preventing infection
• It is essential to ensure children are accurately vaccinated against the deadly poliovirus
• Poliovirus is virtually a thing of the past, thanks to global immunization efforts that have brought us very close to eradicating the illness