Introduction

One in ten children do not receive essential vaccinations, especially in low income areas.¹ Vaccination rates are near-universal in high-income areas, however lower coverage in poorer areas has resulted in this figure, highlighting health inequalities between high and low income countries. 

The eradication of polio depends on filling in the global gaps of vaccination coverage, especially in countries facing poverty, political instability or vaccine hesitancy. Achieving global vaccination targets is the key to eradicating the virus and creating a polio-free future for the world. 

What is polio and why is eradication important?

Polio is short for poliomyelitis, a viral illness caused by the poliovirus and is known to be highly contagious. The virus is spread either through direct contact from person to person, through the faeco-oral route, or through contaminated food and water. Most people infected with polio will not have any symptoms at all and about 1 in 4 people will have flu-like symptoms. These include non-specific flu like symptoms such as fatigue, a sore throat, stomach ache, nausea and headaches.²

Polio mainly affects children under 5 and can spread within hours to the nervous system affecting the brain and spinal cord, making it dangerous. This is where ‘myelitis’ comes from which means inflammation of the spinal cord. This can result in paralysis of limbs and meningitis (an infection of the layer covering the brain and spinal cord).  

According to the World Health Organisation (WHO), 1 in 200 infections lead to paralysis that can not be reversed. Unfortunately, in severe cases, 5-10% of those who are paralysed, will die as a result of paralysis of their breathing muscles.³ According to the US Centers for Disease Control (CDC), 1 to 5 out of 100 people with polio will develop meningitis.²

Historical impact

In the 19th and 20th century, before the development of effective vaccines, polio caused significant fear among parents as well as disability and death in populations. There were many outbreaks in industrialised countries, particularly North America and Europe. 

• The 1916 US epidemic in New York: This was one of the earliest and also one of the most severe outbreaks. While preventative measures such as quarantining and closure of schools and public places were set, the outbreak resulted in 27,000 cases and 6,000 deaths. Due to this outbreak in New York, there was much effort by public health officials to understand transmission and reduce case numbers^{4, 5} 
• Post WW2 epidemics: Polio cases reached its infection peak between the late 1940’s and early 1950’s. In 1952, there were 58,000 cases in the US with thousands of people becoming paralysed. President Franklin D. Roosevelt contracted polio during this time as an adult, raising more awareness of polio. The efforts during this period led to the development of the first successful polio vaccine by Dr. Jonas Salk in the 1950s​⁵

What are the types of poliovirus and the types of vaccines available?

There are two types of polio vaccines that are available, oral polio vaccine (OPV) and inactivated polio vaccine (IPV). Since 1988, global initiatives aimed to give children the OPV vaccine have successfully resulted in wild poliovirus cases reducing by 99.9%. Wild polio refers to the naturally occurring form of poliovirus. The vaccine is safe and stops person-to-person transmission of polio. However, very rarely, in under-vaccinated areas, the live weakened virus in OPV mutates into the other type of poliovirus, known as circulating vaccine-derived poliovirus (cVDPV). ⁶

OPV is used more commonly in low-resource countries because it is given as oral drops, easing administration as it does not require training of healthcare professionals. It also creates stronger immunity than the IPV. 

The IPV is an injection, thus requiring trained staff for administration and so it is used more commonly in high-income countries. The IPV is a dead form of the virus and is safer for immunocompromised individuals, however as mentioned above, the OPV creates stronger immunity.

Both vaccines are part of the global effort to eradicate polio and many countries employ a mixed strategy, maximising the benefits of each one. 

Global vaccination coverage rates

According to the WHO, in 2023, the global vaccination coverage rate of polio in infants (receiving at least three doses of polio vaccine) is around 83%.⁷ This is within the 80-85% range needed to ensure herd immunity.⁸

Herd immunity refers to indirect protection from infectious diseases that occurs when a significant portion of the population has become immune from a disease either due to infection or vaccination. The percentage of vaccine coverage needed for herd immunity differs for different conditions depending on how infectious they are. It is also important for local averages to be within the 80-85% range (rather than relying on global averages) for herd immunity to be effective.⁸

Africa

Polio vaccination rates in Africa have been improving but are still inconsistent. In 2022, the overall vaccination coverage for three doses of the polio vaccine was around 76%, with some countries, like Nigeria, reporting lower rates in certain regions. For instance, the northeastern states of the country have historically faced challenges, with coverage as low as 62%.⁹ 

Asia

In Asia, polio vaccination rates vary significantly. Afghanistan and Pakistan, are the last two countries in the world with endemic polio.¹⁰ In 2014, India was declared polio free. The country was once deemed one of the hardest countries to eradicate polio in. In the 1970s, 200,000 people a year used to die from polio in India.^11,12 With strong support from their government, Bollywood celebrities and mass vaccine campaigns, an inspirational milestone was achieved for the nation.  

Europe

2002 marked the year when the WHO European Region was declared polio free.¹³ However, some regions, especially in Eastern Europe, have reported a decline in all childhood vaccine uptake due to vaccine hesitancy or conflict. For example, countries such as Ukraine, Georgia and Romania have faced challenges with rates of vaccine coverage dropping, causing public health concerns.^14,15

The Americas

The Americas were declared polio free in early 1994, being the first region in the world to do so.¹⁶ Some countries such as Venezuela and Haiti have lower levels of vaccine coverage due to social, economic and political instability.¹⁷ In the case of Haiti, cholera outbreaks have further strained an already struggling health services.¹⁸

Barriers to achieving 100% global vaccination coverage

As seen from the varying levels of vaccination coverages in the world, social, political and economic instability create ongoing barriers to ensuring high rates of vaccine uptake. Other issues include:

• Vaccine Supply Chain Issues: Problems with distribution and logistics in remote or conflict prone zones
• Misinformation and Vaccine Hesitancy: False information such as the measles, mumps and rubella (MMR) vaccine causing autism have become widespread and discourage parents from vaccinating children.
• Political and Economic Barriers: The influence of government policies and reduced funding towards vaccination. In Eastern Europe, we see far less funding into healthcare than the rest of Europe

Summary

Polio is a life threatening yet very preventable viral illness that mainly impacts children. Rates of polio have dropped significantly since the introduction of the OPV and IPV vaccines. High vaccination coverage is crucial for achieving herd immunity, helping to prevent the spread of poliovirus​. However, barriers such as access to healthcare, misinformation, and political challenges continue to hinder vaccination campaigns all over the world, from the Americas to Europe to Asia​. Efforts continue through global initiatives like the World Health Organization and the Global Polio Eradication Initiative (GPEI) to improve vaccination rates and eradicate polio globally.​

Frequently Asked Questions

What is the current global status of polio vaccination? 

According to the World Health Organisation, in 2023, the global average for polio vaccine coverage was 83%

Why is vaccine coverage important for eradicating polio? 

Low vaccination rates can lead to outbreaks, as seen in areas with political instability or conflict zones. It is also important for vaccine coverage to be high to ensure herd immunity. This is particularly important to protect newborns who are not immunised yet and those who might not be able to get vaccines due to certain medical conditions. 

What are the barriers to achieving high polio vaccination rates?

This can range from economic, social or political instability to low access due to conflict or war zones. Some countries see low funding into healthcare or experience outbreaks of other diseases, further straining their health services. Vaccine hesitancy and the spread of misinformation can also be a big factor causing parents to decide against vaccinating their children.