Brady Collins
There are two types of polio vaccines: the inactivated poliovirus vaccine (IPV) and the oral polio vaccine (OPV). IPV, also known as the Salk vaccine, was developed by Jonas Salk in 1955 and contains a killed or inactivated poliovirus. On the other hand, OPV, also known as the Sabin vaccine, was developed by Albert Sabin and contains a weakened or attenuated live poliovirus. While OPV is no longer used in the United States and many other countries due to the rare risk of causing polio in unvaccinated or immunocompromised individuals, it is still utilized in regions with high infection risks and low vaccination rates.
| Characteristics | Values |
|---|---|
| Type of vaccine | Inactivated poliovirus vaccine (IPV) or Oral poliovirus vaccine (OPV) |
| Virus | IPV contains a killed poliovirus, OPV contains a weakened live poliovirus |
| Administration | IPV is given as an injection, OPV is given orally |
| Effectiveness | IPV produces antibodies in the blood, OPV produces antibodies in the intestine |
| Protection | IPV protects against paralytic disease, OPV can lead to paralysis in under-vaccinated populations |
| Use | IPV is used in countries with a low risk of infection, OPV is used in countries with a high risk of infection |
| Safety | IPV is very safe, OPV has a rare risk of causing polio in unvaccinated people |
| Coverage | IPV is used in the US, Canada, Europe, and other countries, OPV is used in countries with ongoing polio transmission |
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What You'll Learn
The inactivated poliovirus vaccine (IPV)
IPV is highly effective in preventing paralytic disease caused by all three types of poliovirus. It triggers an excellent protective immune response in most people, producing antibodies in the blood that can spot all three types of poliovirus. These antibodies last a long time in the body, providing long-term protection against the disease. When a person is exposed to poliovirus, these antibodies prevent the virus from spreading to the central nervous system and protect against paralysis.
In the United States, IPV has been the only polio vaccine used since 2000. It is part of the routine childhood immunization schedule, with children typically receiving four doses of IPV before or at school entry. IPV may also be given in combination with other vaccines, such as tetanus, diphtheria, and acellular pertussis.
In countries where the risk of poliovirus infection is high, the oral polio vaccine (OPV) may still be used. OPV contains a weakened live virus and is given orally as drops. While OPV has been instrumental in eradicating wild polioviruses, there is a rare risk of it causing polio in under-immunized or immunodeficient individuals. Therefore, countries with a low risk of poliovirus infection, such as the United States, Canada, and Europe, primarily use IPV to protect their populations from polio.
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The oral polio vaccine (OPV)
OPV has been instrumental in eradicating wild polioviruses around the world, including in the United States. It stops the spread of the virus by inducing immunity in the gut, which is the primary site of wild poliovirus entry. OPV provides longer-lasting immunity than the Salk vaccine (IPV), as it provides both humoral immunity and cell-mediated immunity. One dose of trivalent OPV produces immunity to all three poliovirus serotypes in roughly 50% of recipients. Three doses of OPV produce protective antibodies to all three poliovirus types in more than 95% of recipients. As with other live-virus vaccines, immunity initiated by OPV is probably lifelong.
OPV is still used in a few countries where the risk of getting infected with poliovirus is high, as the vaccine is low-cost and easy to administer to large numbers of people. OPV can create immunity in someone who is vaccinated and can sometimes also spread (through a vaccinated person's saliva or faeces) to provide immunity to others nearby.
The main disadvantage of OPV is that, as an attenuated but active virus, it can induce vaccine-associated paralytic poliomyelitis (VAPP) in roughly one individual per 2.7 million doses administered. The live virus can circulate in under-vaccinated populations and, over time, can revert to a neurovirulent form causing paralytic polio. This genetic reversal of the pathogen to a virulent form takes considerable time and does not affect the person who was originally vaccinated. Due to the risk of VAPP, OPV has not been used in the United States since 2000, and many other countries have also discontinued its use.
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The risk of VAPP
The oral poliovirus vaccine (OPV) contains a combination of one, two, or three strains of live, weakened poliovirus. It is given in the form of oral drops and has been instrumental in eradicating wild polioviruses around the world, including in the United States. OPV is no longer used in the United States and many other countries due to the rare risk of causing vaccine-associated paralytic poliomyelitis (VAPP) in people who aren't immunized or who have weakened immune systems.
VAPP is a rare adverse event associated with OPV. It is defined as a case of acute flaccid paralysis (AFP) with residual paralysis occurring in an OPV recipient between 4 and 40 days after the dose of OPV was administered, or in a person who has had contact with a vaccine recipient between 7 and 60-75 days after the dose was given. The risk of VAPP was calculated for each country using two methods: VAPP per million OPV doses and VAPP per million births.
In the United States, from 1980 to 1991, 105 cases of paralytic poliomyelitis were identified, 98 (93%) of which were VAPP, resulting in an average of 8.2 cases per year. The overall risk of VAPP was one case per 2.5 million doses of OPV distributed. Despite the inclusion of previously unidentified VAPP cases, the risk of VAPP has remained relatively constant over time.
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The importance of high vaccination coverage
The oral polio vaccine (OPV) contains a live, weakened poliovirus. OPV is no longer used in the United States and many other countries due to the rare risk of causing polio in unvaccinated individuals or those with weakened immune systems. Instead, the inactivated poliovirus vaccine (IPV), which contains a killed poliovirus, is used. IPV is given as a series of shots and is safe and effective, offering protection to 99-100% of people who receive the recommended doses.
High vaccination coverage is critical in the effort to eradicate polio globally. The World Health Organization (WHO) has included the polio vaccine on its List of Essential Medicines, and the global eradication campaign has relied largely on the OPV developed by Albert Sabin and Mikhail Chumakov. This vaccine has been highly successful, resulting in a 99.9% reduction in global polio incidence.
However, maintaining high vaccination coverage is essential to prevent outbreaks, especially in areas with low vaccination rates and poor sanitation. When there is insufficient vaccination coverage, the weakened strain of the poliovirus from OPV can spread among under-immunized populations, mutate, and cause illness and paralysis. This is known as a vaccine-derived poliovirus (VDPV).
To address this issue, the United States switched from OPV to IPV in 2000, and other countries with high immunization coverage and low risk of importation are advised by the WHO to follow a similar vaccination schedule. By achieving and maintaining high vaccination coverage with IPV, countries can protect their populations from both naturally occurring polioviruses and VDPVs.
Additionally, high vaccination coverage helps prevent the importation of wild polioviruses into previously polio-free regions. This is crucial, as the transmission of wild poliovirus continues to pose an ongoing risk. Therefore, it is recommended that individuals travelling to high-risk areas ensure they have received the appropriate polio vaccine doses, as outlined by the CDC and other health organizations.
In summary, high vaccination coverage is vital to protect individuals and communities from polio and its potentially devastating consequences. By achieving high coverage, we can maintain the significant progress made in eradicating polio globally and ensure that future generations are safeguarded from this disease.
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OPV's role in containing polio outbreaks
The oral polio vaccine (OPV) is a live, attenuated vaccine developed by physician and microbiologist Albert Sabin. It contains a weakened version of one, two, or three strains of poliovirus and is administered orally as drops or on a sugar cube. OPV has played a crucial role in containing polio outbreaks worldwide, including in the United States. Its ability to induce mucosal immunity and interrupt the chain of transmission has made it a powerful tool in stopping polio outbreaks.
The effectiveness of OPV in containing polio outbreaks is evident in the global eradication of wild poliovirus type 2 (WPV2) in 2015 and wild poliovirus type 3 (WPV3) in 2019. OPV has contributed significantly to these achievements by interrupting the transmission of the virus and inducing immunity in vaccinated individuals. As a result, the world transitioned from trivalent OPV (protecting against all three types of poliovirus) to bivalent OPV, which targets poliovirus types 1 and 3.
However, it is important to address the limitations of OPV. In rare instances, if OPV is allowed to circulate in under-immunized or unimmunized populations for an extended period, the weakened virus can revert to a form that causes illness and paralysis. These mutated strains are known as vaccine-derived polioviruses (VDPVs) or circulating vaccine-derived polioviruses (cVDPVs). VDPVs can cause outbreaks in regions with low vaccine coverage or immunodeficient individuals, underscoring the importance of maintaining high vaccination rates to prevent such occurrences.
Despite this limitation, OPV remains a valuable tool in containing polio outbreaks, especially in regions with high infection risks. Its oral administration and ability to induce mucosal immunity make it a practical and effective solution in the ongoing fight against polio. By achieving high OPV vaccination coverage, countries can effectively contain and eradicate polio outbreaks, protecting their populations from this crippling and potentially deadly disease.
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Frequently asked questions
There are two types of polio vaccines: the inactivated poliovirus vaccine (IPV) and the oral polio vaccine (OPV). IPV does not contain a live virus, while OPV contains a weakened live virus.
IPV is given as a series of shots and is the polio vaccine used in the United States, Canada, Europe, and many other countries where the risk of getting infected with poliovirus is low.
OPV is still used in a few countries where the risk of getting infected with poliovirus is high because the vaccine is low-cost and easy to administer to a lot of people. OPV is no longer used in the United States and many other countries due to the rare risk of causing polio in unvaccinated individuals or those with weakened immune systems.
