The recent confirmation of a polio case in a two-year-old child from West Garo Hills district in Meghalaya has sparked significant concern across India. This development is particularly alarming because India was declared polio-free by the World Health Organisation (WHO) in 2014, with the last known case reported in 2011. However, the current case is not due to wild polio but a less-known variant called vaccine-derived polio.
What Is Vaccine-Derived Polio?
Poliomyelitis, commonly known as polio, is a highly infectious disease caused by the poliovirus. This virus is typically transmitted through the fecal-oral route, often by ingesting contaminated food or water. Polio is notorious for its ability to cause paralysis and, in some cases, can be life-threatening.
The poliovirus manifests in a variety of symptoms, including fatigue, fever, headache, vomiting, diarrhoea or constipation, sore throat, neck stiffness, pain or tingling sensations in the arms and legs, severe headaches, and sensitivity to light (photophobia). The virus has three different strains: wild poliovirus type 1 (WPV1), wild poliovirus type 2 (WPV2), and wild poliovirus type 3 (WPV3). Despite their differences, these strains present identical symptoms.
Historically, most polio cases have been due to wild poliovirus. However, with the launch of the Global Polio Eradication Initiative in 1988, which aimed to provide equitable vaccine access, the incidence of wild poliovirus cases has dramatically decreased. India was declared polio-free in 2014, and by 2023, only 12 cases of paralysis caused by wild poliovirus were reported worldwide, limited to Pakistan and Afghanistan.
The Rise of Vaccine-Derived Polio Cases
While the number of wild poliovirus cases has dropped, another form of polio, known as vaccine-derived polio, has become more prominent. This type of polio arises from the use of the Oral Polio Vaccine (OPV), which contains a weakened form of the virus. Although this vaccine is designed to stimulate an immune response without causing the disease, it can, in very rare cases, lead to what is known as vaccine-associated paralytic poliomyelitis (VAPP).
After receiving the OPV, the weakened virus is excreted in the stool and can spread to others. In communities with low immunity levels, this virus can mutate and potentially circulate, leading to cases of paralysis. The current case in Meghalaya is an example of this rare occurrence, where the vaccine-derived virus has led to a confirmed case of polio in a child.
Types of Polio Vaccines
Understanding the different types of polio vaccines is crucial to grasping the situation. There are two primary types of polio vaccines:
1. Oral Polio Vaccine (OPV)
The Oral Polio Vaccine (OPV) is the most widely used vaccine in India. It contains a weakened version of the poliovirus, which is administered orally, typically in the form of drops. OPV is commonly used in mass immunization campaigns, such as the National Immunization Days (NIDs), and is favored for its ease of administration.
However, due to its live, weakened virus content, OPV can replicate in the body. In rare cases, this can lead to VAPP, especially in communities where immunity levels are low.
2. Inactivated Polio Vaccine (IPV)
The Inactivated Polio Vaccine (IPV), on the other hand, contains a killed version of the poliovirus and is administered via injection. IPV is part of the routine immunization schedule in India and is often given alongside other vaccines in combination shots. Unlike OPV, IPV does not contain a live virus, which means it cannot cause VAPP.
In India, both OPV and IPV are used, with OPV being the preferred choice for mass immunization due to its ease of use. However, the rare risk of vaccine-derived polio associated with OPV has led to increasing discussions about the broader use of IPV.
The Implications of the Meghalaya Case
The confirmation of a vaccine-derived polio case in Meghalaya has raised several critical questions and concerns. While this type of polio is rare, it highlights the need for ongoing vigilance in vaccination efforts, even in countries declared polio-free. The WHO has been alerted, and an investigation is currently underway to determine the extent of the situation.
Why Is Vaccine-Derived Polio a Concern?
Vaccine-derived polio is particularly concerning because it can occur in areas with low immunity levels. This means that even in a polio-free country like India, if vaccination rates drop or immunity wanes in certain populations, the weakened virus from OPV can mutate and spread, potentially leading to new cases of polio.
The Role of Immunization in Preventing Polio
The key to preventing both wild and vaccine-derived polio lies in maintaining high levels of immunization. The more people are vaccinated, the less likely it is for the virus to circulate and mutate. This is why mass immunization campaigns like the National Immunization Days (NIDs) are so important.
In the case of Meghalaya, ensuring that the population is adequately vaccinated is essential to prevent further cases. Public health authorities must also continue to monitor the situation closely and take swift action to contain any potential spread.
Vigilance and Immunization Are Key
The case of vaccine-derived polio in Meghalaya serves as a stark reminder that the fight against polio is not over, even in countries that have been declared polio-free. While the risk of vaccine-derived polio is low, it underscores the importance of maintaining high immunization rates and ensuring that no child is left unvaccinated.
As India continues its efforts to keep polio at bay, it is crucial to remain vigilant and proactive in addressing any new challenges that arise. The WHO’s investigation into the Meghalaya case will be critical in understanding how to prevent similar cases in the future and ensuring that India remains polio-free.
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