Acute Flaccid Paralysis surveillance as a crucial defence against polio in India | Explained

India needs to continue efforts to maintain its polio-free status, and AFP surveillance has to remain a cornerstone of its strategy

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India’s polio-free status, declared in 2014, is a significant global health achievement. However, polio remains a threat, as seen in 2024 when a case of vaccine-derived poliovirus surfaced in Meghalaya, following several years without any local cases. Around the same time, the Gaza Strip reported its first paralytic polio case in 25 years, further demonstrating the lingering risks in conflict-hit regions with fragile healthcare systems or gaps in immunisation coverage. The second round of an emergency polio vaccination campaign was started on October 14 in Gaza to vaccinate an estimated 5 lakh children under ten years with a second dose of the novel oral polio vaccine type 2 (nOPV2) vaccine. These outbreaks have renewed attention to the importance of Acute Flaccid Paralysis (AFP) surveillance in India that serves as an early warning system for poliovirus circulation and is crucial to maintain India’s polio-free status.

What is Acute Flaccid Paralysis (AFP)?

Acute Flaccid Paralysis refers to the sudden onset of weakness or paralysis in one or both limbs without any prior injury or trauma. AFP is a clinical syndrome that is an early indicator for diseases like poliomyelitis (polio). Poliovirus is the most concerning cause of AFP, as the virus can cause irreversible paralysis and, in some cases, death. 

In India, any child under 15 who shows symptoms of AFP is immediately investigated to determine whether the paralysis is due to poliovirus or other causes. The differential diagnosis of acute flaccid paralysis includes Guillain-Barré syndrome and transverse myelitis. Less common aetiologies are traumatic neuritis, encephalitis, meningitis and spinal cord compressing tumours.

Investigating AFP cases is essential to differentiate between polio and other causes of paralysis. This allows for early detection of potential poliovirus circulation and quick response to prevent outbreaks.

Acute Flaccid Paralysis (AFP) typically manifests through weakness in one or more limbs, often accompanied by a loss of muscle tone (flaccidity), where the affected limbs become limp. In more severe cases, individuals experience difficulty in movement, which may progress to complete paralysis. Interestingly, most cases of AFP present without pain in the paralyzed limbs, differentiating it from other forms of paralysis caused by trauma or injury. 

Also read: ​Intriguing silence: On the case of polio in India, delayed official response

Why is AFP surveillance important ?

AFP surveillance is a cornerstone of polio eradication efforts as it enables the early detection of poliovirus, even in areas where no symptomatic cases have been identified. The World Health Organization (WHO) mandates that countries committed to polio eradication implement stringent AFP surveillance systems to ensure the virus can be detected and managed before it spreads further. With its vast and densely populated regions, this surveillance is important for India to safeguard its progress in eradicating polio.

The 2024 outbreak in Meghalaya demonstrated that even in areas with robust immunisation programmes, vigilance is required to prevent outbreaks from vaccine-derived polioviruses, which can occur when live oral polio vaccines mutate. Maintaining strong AFP surveillance ensures the country can respond swiftly to such threats.

What constitutes AFP surveillance?

Environmental surveillance, particularly testing sewage water for poliovirus, complements AFP case detection by identifying silent virus transmission in communities. This method is especially useful in heavily populated areas where poliovirus can circulate unnoticed. Environmental sampling played a key role in identifying the virus in both Gaza and parts of India, allowing health authorities to act quickly, even before clinical cases emerged.

AFP involves a coordinated network of health workers, hospitals, laboratories, and environmental surveillance units to detect, report, and investigate any signs of AFP. When a case of acute flaccid paralysis (AFP) is detected in a child under 15 years old, it is immediately reported to the health authorities to begin the investigative process. The system can be alerted by various sources. Healthcare workers, often the first point of contact, report any suspected cases of AFP based on symptoms observed in the patient. Community members, especially in remote areas, also play a critical role in informing local health authorities if they see individuals exhibiting signs of paralysis. Laboratories are another key component, notifying authorities if poliovirus is detected in stool samples collected from suspected cases. This multi-layered reporting system ensures swift detection and action.

When a case of AFP is suspected and reported, health workers conduct a detailed investigation within 48 hours, collecting clinical information and stool samples for laboratory testing. Two stool samples are collected from the affected individual within 14 days of the onset of paralysis. These stool samples are tested in one of India’s WHO-accredited laboratories to check for wild and vaccine-derived poliovirus and other non-polio enteroviruses that could be responsible for the paralysis. Health workers visit the patient’s home to verify the onset of symptoms and determine whether anyone in close contact with the patient could have been exposed. A follow-up examination is conducted 60 days after the initial report to determine whether the patient has residual paralysis. This helps distinguish polio from other causes of AFP. 

If poliovirus is detected, the system initiates a rapid response. A targeted vaccination campaign, known as a “mop-up operation,“ is launched in the affected area to halt further virus transmission. 

In addition, the system geographically maps reported AFP cases, flagging areas where clusters of cases are found, thus allowing for targeted investigation and intervention. This meticulous approach has allowed India to maintain robust polio surveillance and swiftly respond to any signs of virus circulation, ensuring the country remains polio-free. The Indian government, in collaboration with the WHO, the National Polio Surveillance Project, has ensured that AFP surveillance covers even the most remote regions. This robust system played a pivotal role in detecting the last polio case in India in 2011, allowing the country to implement rapid responses and maintain its polio-free status. The Integrated Disease Surveillance Program (IDSP) works alongside AFP surveillance to strengthen disease monitoring in India.

What is the future course of action?

While India has been polio-free since 2011, poliovirus continues to circulate in parts of the world, notably Afghanistan and Pakistan, where the virus remains endemic. The Global Polio Eradication Initiative (GPEI), spearheaded by the WHO and UNICEF, stresses the importance of maintaining high levels of AFP surveillance and routine vaccination in all countries. Countries that have successfully eradicated polio, like India, must remain on guard, as the virus can re-enter through migration or vaccine-derived strains, as seen in 2024.

AFP surveillance remains a cornerstone of India’s strategy to prevent the return of poliovirus. Through its surveillance system, India should detect, investigate, and respond quickly to any case of AFP, ensuring that poliovirus is kept at bay. The recent outbreaks in Meghalaya and Gaza are reminders that constant vigilance is necessary to prevent the reintroduction of the virus. 

As we move closer to the goal of global polio eradication, AFP surveillance will continue to play a critical role in protecting populations from this crippling disease.

(Dr. C. Aravinda is an academic and a public health physician. aravindaaiimsjr10@hotmail.com)

Published - October 23, 2024 02:26 pm IST