Two vaccines that brought us to the brink of eradicating polio

• The poliovirus has only one natural host - humans - and many of the early strains of the virus were isolated from humans and wouldn’t infect non-human primates.
• Since scientists kept passing the virus through the brain tissues of macaques, it adapted to that mode of infection.

Eradication target missed

• Polio eradication is one of the top priorities of the World Health Organisation (WHO).
• Since Africa was declared polio-free in August 2020, the wild poliovirus has been restricted to rural pockets of Afghanistan and Pakistan.
• But according to a recent report in Science, the virus is beginning to reappear in big cities in these two countries.
• This reemergence is a result of vaccine hesitancy due to misinformation, conflict, poverty, and limited access to these isolated regions.
• The WHO’s Global Polio Eradication Initiative is thus set to miss its deadline of eradicating polio by the end of 2024.
• The immune system has two main parts: the systemic and the mucosal.
• The systemic component includes the blood, the brain, and all other organ systems.
• The mucosal component includes the inner linings of the digestive and respiratory systems, the urogenital tract, and the eyes.
• These regions are lined with mucous membranes that provide an additional layer of protection, as they frequently come into contact with the external environment.
• Since the OPV went into the stomach, it induced a powerful protective mucosal immune response right where the virus would have to begin its infection.

Advantage of OPV over IPV

• The OPV had multiple advantages over the IPV.
• First, the vaccine induced a protective response at the viral entry site — the gut— allowing it to provide a much greater degree of protection relative to the IPV.
• Second, the OPV was administered orally and didn’t require syringes or trained personnel for its administration.
• The world has used both vaccines in the fight against polio. While some countries, such as Norway, Sweden, Finland, and Iceland, relied exclusively on the IPV, most countries have used a combination of the two.
• The latter countries prefer the OPV for its superior protection and ease of administration. When the number of natural polio cases drops to zero, they switch to IPV for its enhanced safety.