Rare polio case reported in Meghalaya: What is it and is this a cause of concern?

Govt says it is vaccine-derived. India continues to be polio-free unless cases of wild polio virus infection are detected

A vaccine-derived poliovirus is a strain related to the weakened form of the virus that is used in the oral polio drops for immunisation.

The news of a two-year-old child from Meghalaya testing positive for polio, a highly infectious viral disease that may even lead to fatal paralysis, has raised concern. However, Health Ministry officials said the case was vaccine-derived and there was no need to be alarmist about it.

 

While this case does not jeopardise India’s polio-free status, the West Garo hills area, where the case was detected, is on high alert to ensure that the infection does not spread.

 

What is vaccine-derived polio infection?

A vaccine-derived poliovirus is a strain related to the weakened form of the virus that is used in the oral polio drops for immunisation. While the vaccine is safe — and has led to most countries in the world successfully eradicating the infection — it can on occasion trigger the disease in children who have a weakened immune system. While activating an immune response in the body, the vaccine-virus can get excreted, and over time in the bloodstream, can change genetically.

 

 “The oral polio vaccine can lead to vaccine-derived polio strains in two ways. One, the weakened virus can continue circulating from child to child, gaining back its ability to transmit quickly and cause severe infection every time it spreads. Two, the vaccine virus can cause chronic infection in children with weakened immune systems, replicating in their gut for years and slowly gaining its ability to cause severe infection. In the Meghalaya case, it seems like the virus replicated within one child. It is easier to control further spread of such vaccine-derived variants because the other children in the area are likely fully immunised,” said Dr T Jacob John, former professor of virology at Christian Medical College Vellore.

 

He said, “One in every 150,000 children given the vaccine in India gets the infection from it.” So even if children in the area are completely vaccinated, health workers would have to immunise them again as a preventive measure.

 

Have vaccine-derived polio cases been detected in India before?

India’s last case of wild poliovirus — infection caused by the naturally occurring virus — was detected in West Bengal’s Howrah district in 2011. After successfully preventing any wild polio infections for three years, the country was declared polio-free in 2014.

 

Vaccine-derived polio cases have, however, been reported during this period. An 11-month- old immuno-deficient child from Maharashtra’s Beed district died of vaccine-derived polio in 2013. It was also reported in a 2.5-year-old child from Delhi. Vaccine-derived polio virus was detected in sewage samples in Kolkata in 2022. These are not the only incidents of vaccine-derived polio cases in India.

 

Does it change India’s polio-free status?

India continues to be polio-free unless cases of wild polio virus infection are detected.

 

Why was the oral polio vaccine rolled out in 2016?

There are three types of polio virus that cause infections in humans. The weakened forms of all these viruses were included in the oral polio vaccine. With polio vaccine campaigns across the world leading to the eradication of type 2 wild poliovirus in 1999 — and 90 per cent of the circulating vaccine-derived polio infections were caused by type 2 till 2019 — the decision was taken to switch the vaccines from trivalent to bivalent in 2016. A coordinated effort across the globe ensured that the vaccine from one region did not cause vaccine-derived infections in other parts of the world.

 

Why have health experts been asking to shift to the inactivated poliovirus vaccine (IPV) regime?

 

While the oral polio vaccine is extremely effective in preventing the spread of the infection from one individual to another and is easy to administer, it could cause the infection itself in rare cases. Not only that, this infection can then also spread to others. Hence, the plea for IPV regimes.

 

One of the challenges with IPV is that it can only protect an individual from infection but cannot prevent transmission. However, with no live virus, it cannot cause infection. This means a high level of immunisation has to be maintained to prevent any future outbreaks.

 

Countries such as Canada and the US have already moved completely to IPV. India still uses both — IPV is administered to children during routine immunisation while oral polio vaccine is given to children up to the age of five years.

https://indianexpress.com/article/health-wellness/rare-polio-case-reported-meghalaya-cause-concern-9525936/