Global Polio Resurgence and Reevaluating Basics

Sub: Sci

Sec: Health

Why in News

The resurgence of polio globally, with environmental samples and human cases detecting both wild poliovirus (WPV) and vaccine-derived poliovirus (cVDPV), highlights the fragility of global health achievements.

Current Situation:

WHO reported poliovirus detection in wastewater in Finland, Germany, Poland, Spain, and the UK (2024). No confirmed cases yet, but the findings emphasize vaccination and surveillance.
Pakistan: 4 WPV1 cases, 8 positive samples.
Africa: Cases detected in Cameroon, Côte d’Ivoire, Chad, and Nigeria.

About Polio (Poliomyelitis):

Polio is a highly infectious viral disease caused by the poliovirus, primarily affecting children under the age of 5.
The virus spreads predominantly through the faecal-oral route, often via contaminated water or food, and can also transmit through oral-oral contact.
Symptoms:
- Approximately 70% of infections are asymptomatic.
- Around 25% present mild symptoms such as fever, fatigue, headache, vomiting, stiffness in the neck, and pain in the limbs.
- A small proportion of cases lead to irreversible paralysis, typically in the legs. Among those paralyzed, 5–10% may die due to immobilization of breathing muscles.
Prevention: Polio is preventable through vaccination. The two primary vaccines are:
- Inactivated Poliovirus Vaccine (IPV): Administered via injection; contains inactivated virus.
- Oral Poliovirus Vaccine (OPV): Administered orally; contains a live, attenuated (weakened) virus.

About Wild Poliovirus (WPV):

Wild polioviruses are naturally occurring strains of poliovirus circulating in the environment.
Serotypes:
- Type 1: The only wild poliovirus strain still in circulation as of 2024.
- Type 2: Declared eradicated in September 2015; last detected in India in 1999.
- Type 3: Declared eradicated in October 2019; last detected in November 2012.
As of 2024, wild poliovirus type 1 remains endemic in two countries: Pakistan and Afghanistan.

About vaccine-derived poliovirus (VDPV):

Vaccine-Derived Poliovirus (VDPV) refers to strains of poliovirus that originate from the oral polio vaccine (OPV).
While OPV effectively protects against poliovirus, it contains live, attenuated (weakened) virus strains that can occasionally revert to a virulent form, leading to cases of paralysis.

Classification of VDPV:

WHO classifies VDPV cases into three categories:

Circulating Vaccine-Derived Polioviruses (cVDPVs): Emerges in populations with low vaccination coverage, where the vaccine virus can spread among unvaccinated individuals.
Immune-Deficiency Associated VDPV (iVDPV): Occurs in individuals with primary immunodeficiencies who may excrete the vaccine-derived virus for an extended period, sometimes years.
Ambiguous Vaccine-Derived Polioviruses (aVDPVs): Cases where it is unclear if the virus is derived from vaccine strains or has characteristics of both wild and vaccine strains.

Polio in India:

India was declared polio-free in 2014, marking a significant public health achievement.
Prior to eradication, India conducted extensive vaccination campaigns, delivering around 1 billion doses of polio vaccine to 172 million children each year over four years leading up to the last reported case.
Post-eradication, India continues to maintain high immunization coverage to prevent reintroduction of the virus.