Logan Reed
Polio is a highly infectious disease that affects the nervous system and can lead to paralysis and even death. It was once one of the most feared diseases, especially in industrialized countries, where it paralysed hundreds of thousands of children annually. The development of vaccines in the 1950s and 1960s helped bring the disease under control and practically eliminated it as a public health issue in these countries. However, polio continues to affect other regions, and maintaining high levels of vaccination coverage is crucial to prevent outbreaks, especially in areas with low vaccination rates and poor sanitation. While the inactivated polio vaccine (IPV) protects the vaccinated individual, the oral polio vaccine (OPV) interrupts poliovirus transmission, making it a powerful tool to stop outbreaks.
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What You'll Learn
The success of the polio vaccine in different countries
The success of the polio vaccine is evident in the reduction of polio cases globally. In 1988, the World Health Assembly aimed to eradicate polio, and since then, significant progress has been made. The two types of vaccines, inactivated polio vaccine (IPV) and oral polio vaccine (OPV), have played a crucial role in this achievement.
The first successful polio vaccine was created by Jonas Salk in the early 1950s. His inactivated polio vaccine (IPV) was licensed in 1955, and by 1961, annual cases in the United States had dropped significantly. This vaccine was not approved for use in the United States, but it successfully controlled the spread of polio in other countries.
The oral polio vaccine (OPV), developed by Albert Sabin, came into commercial use in 1961. OPV has been particularly effective in interrupting the chain of poliovirus transmission, making it a powerful tool to stop polio outbreaks. Hungary adopted OPV in December 1959, and Czechoslovakia in early 1960, becoming the first country in the world to eliminate polio. In 1962, Cuba also began administering OPV nationwide, contributing to the eradication of polio in the Americas by 1994.
The World Health Organization's (WHO) efforts in the 21st century have been remarkable. The number of countries where polio remained endemic decreased from 6 in 2003 to 4 in 2006. By 2014, the WHO's South-East Asia region was certified polio-free, followed by the African region in 2020. As of July 2021, only two cases of wild poliovirus had been recorded globally that year, one each in Afghanistan and Pakistan.
While great strides have been made, maintaining high levels of vaccination coverage is crucial. Some countries, like Pakistan and Afghanistan, have resisted polio vaccination programs, and the risk of importation of wild poliovirus into previously polio-free regions remains. The emergence of circulating vaccine-derived poliovirus (cVDPV) has also led to the development of novel oral polio vaccines to enhance safety and prevent further outbreaks.
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The development of the polio vaccine
The development of a polio vaccine was a significant breakthrough in the history of medicine, and the efforts to create one began as early as the 1930s. The first formal presentation of a polio vaccine was made by Kolmer in November 1935, where he reported on the vaccination of 446 children and adults with his attenuated vaccine. However, his work was not without controversy, as he did not provide adequate instructions or monitoring for the experimental program, and over 10 cases of paralytic polio were reported following vaccination.
A significant advancement was made in 1949 when John Enders, Thomas Weller, and Frederick Robbins successfully cultivated poliovirus in human tissue at Boston Children's Hospital. Their achievement paved the way for the safe and large-scale production of viral vaccines. In the same year, Hilary Koprowski demonstrated the first successful polio vaccine, which was a live attenuated virus that people drank. However, this vaccine was not approved for use in the United States.
The first inactivated polio vaccine (IPV) was developed by Jonas Salk in 1953 using a virus grown on monkey kidney cells and inactivated with formalin. Salk tested his vaccine on himself and his family in 1953, and by 1954, it was being tested in a placebo-controlled trial on 1.6 million children in Canada, Finland, and the United States. On April 12, 1955, the results were announced, and Salk's vaccine was licensed and adopted throughout the United States. This vaccine played a crucial role in reducing the incidence of polio, with annual cases dropping from 58,000 to 5,600 by 1957.
In 1956, Albert Sabin developed the live-attenuated oral polio vaccine (OPV), which came into commercial use in 1961. Unlike the IPV, the OPV could interrupt the chain of transmission, making it a powerful tool to stop polio outbreaks. This vaccine was also crucial in the global effort to eradicate polio, and by 1962, Cuba had begun administering OPV in nationwide immunization programs.
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The impact of the polio vaccine on the spread of polio
Polio is a highly infectious disease that mostly affects young children. It attacks the nervous system and can lead to spinal and respiratory paralysis and, in some cases, death. Before the polio vaccine was available, several polio epidemics occurred between 1948 and 1955. Many people avoided public gatherings and fairs, and parents would not let their children play with new friends. Some people with polio whose breathing muscles were paralyzed were placed in large machines called iron lungs, which helped them breathe and may have helped them live longer.
The first successful demonstration of a polio vaccine was by Hilary Koprowski in 1950, with a live attenuated virus that people drank. However, this vaccine was not approved for use in the United States. In 1955, Jonas Salk developed the first vaccine against polio, an injectable, inactivated (killed) polio vaccine (IPV). By 1957, annual cases dropped from 58,000 to 5,600, and by 1961, only 161 cases remained. However, while IPV protected the vaccinated individual, it did not stop the poliovirus from spreading between people.
In 1961, Albert Sabin developed a "live" oral polio vaccine (OPV), which rapidly became the vaccine of choice for most national immunization programs worldwide. OPV, unlike IPV, interrupted the chain of transmission, meaning that this vaccine could stop polio outbreaks in their tracks. In 1962, Cuba began to administer OPV in nationwide immunization programs. Since 2000, only IPV has been used in the United States to eliminate the risk of polio variants that can occur with OPV. However, OPV is still used in other countries.
Thanks to successful vaccination programs, polio has been eliminated in many parts of the world, including the Americas and Europe. However, polio still occurs in other parts of the world, such as Africa, Asia, and the Middle East, and there is an ongoing risk of importation into previously polio-free regions. As of October 2022, naturally acquired polio is only found in Afghanistan and Pakistan. To maintain polio-free status, high levels of vaccination coverage must be maintained.
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The importance of maintaining high levels of vaccination coverage
The success of vaccination programmes in controlling the spread of polio is evident. The introduction of vaccines in the 1950s and 1960s brought polio under control and practically eliminated it as a public health problem in industrialized countries. The highly infectious disease, which mostly affects young children, attacks the nervous system and can lead to paralysis and even death.
The development of vaccines by Jonas Salk and Albert Sabin played a pivotal role in curbing the disease. Salk's inactivated polio vaccine (IPV) was licensed in 1955, and by 1961, annual cases had dropped drastically. Sabin's oral polio vaccine (OPV), which became the vaccine of choice for most national immunization programmes, was crucial in interrupting the chain of poliovirus transmission. This distinction is important because while IPV protected the vaccinated individual, it did not prevent the virus from spreading between people.
Despite these successes, maintaining high levels of vaccination coverage is essential for several reasons. Firstly, polio still occurs in parts of the world, and it only takes one infected traveller to reintroduce the disease to previously polio-free regions. This risk is heightened in areas with low vaccination coverage and poor sanitation. Secondly, while wild poliovirus has been eliminated in some regions, outbreaks of vaccine-derived poliovirus can still occur. This strain emerges when the live oral polio vaccine mutates and reverts to causing poliomyelitis. Developing novel oral polio vaccines, such as nOPV2, aims to address this challenge and stop further outbreaks.
Thirdly, routine immunization is crucial in protecting against both wild and vaccine-derived polioviruses. Ensuring that all children receive the recommended doses of the polio vaccine is vital, as those who are unvaccinated or partially vaccinated remain at risk of contracting the disease. Finally, maintaining high vaccination coverage is essential for global polio eradication efforts. The World Health Assembly's resolution to eradicate polio in 1988 and the establishment of the Global Polio Eradication Initiative demonstrate a commitment to achieving permanent reduction to zero. Maintaining momentum in immunization campaigns is critical to fulfilling this goal.
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The eradication of polio in the Americas
Poliomyelitis, or polio, is a highly infectious disease that mostly affects young children and attacks the nervous system, causing spinal and respiratory paralysis and, in some cases, death. The first successful demonstration of a polio vaccine was in 1950, with a live attenuated virus that people drank. The success of an inactivated (killed) polio vaccine, developed by Jonas Salk, was announced in 1955. Another attenuated live oral polio vaccine, developed by Albert Sabin, came into commercial use in 1961.
Following the widespread use of the poliovirus vaccine in the mid-1950s, the incidence of poliomyelitis declined rapidly in many industrialized countries. In 1962, Cuba began using the oral vaccine in a series of nationwide polio campaigns. The early success of these mass vaccination campaigns suggested that polioviruses could be globally eradicated. The Pan American Health Organization (PAHO), under the leadership of Ciro de Quadros, launched an initiative to eradicate polio from the Americas in 1985.
In 1988, the World Health Organization (WHO), together with Rotary International, UNICEF, and the U.S. Centers for Disease Control and Prevention (CDC) passed the Global Polio Eradication Initiative (GPEI), with the goal of eradicating polio by the year 2000. The last case of wild poliovirus poliomyelitis in the Americas was reported in Peru in August 1991. On 20 August 1994, the Americas were certified polio-free by the WHO. This achievement was a milestone in efforts to eradicate the disease.
The early detection of cases through robust surveillance of acute flaccid paralysis (AFP) in children under 15 years of age and high vaccination coverage were key to keeping the Americas free of polio for decades. However, the 2022 detection of a vaccine-derived polio case in New York raised alarms among public health authorities worldwide, and there is a renewed call to improve immunization rates.
In summary, the eradication of polio in the Americas was achieved through the development of effective vaccines, mass vaccination campaigns, and robust surveillance systems. However, maintaining high immunization rates and early detection of cases remain crucial to prevent the re-emergence of this devastating disease.
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Frequently asked questions
Yes, polio vaccines have successfully interrupted poliovirus transmission in most parts of the world.
There are two types of polio vaccines: inactivated polio vaccine (IPV) and oral polio vaccine (OPV).
The polio vaccine is safe and effective in preventing poliomyelitis. The vaccine is estimated to be 80-90% effective against paralytic polio.
The first successful demonstration of a polio vaccine was by Hilary Koprowski in 1950. However, it was not approved for use in the United States. Jonas Salk developed the first licensed inactivated polio vaccine (IPV) in 1955.
While polio has been eliminated in most parts of the world, it still occurs in certain regions. As of October 2022, naturally acquired polio cases are only found in Afghanistan and Pakistan. Therefore, maintaining high levels of vaccination coverage is crucial to prevent outbreaks in previously polio-free regions.
