The two vaccines that brought us to the brink of eradicating polio

Sub: Science and tech

Sec: Health

Context:

The wild poliovirus is restricted to pockets of Afghanistan and Pakistan, and is beginning to reappear from here in big cities in these two countries.

About Polio:

Polio is also called Poliomyelitis.
It is a viral disease that destroys the nerve cells present in the spinal cord, causing paralysis or muscle weakness to some parts of the body.
It is a contagious disease affecting the nervous system and is caused by Picornaviridae – a poliovirus.
The virus is transmitted by person-to-person through the following ways –
- 1) Through the fecal-oral route.
- 2) By contaminated water or food.
This virus primarily grows and multiplies in the intestine, from where it can attack the nervous system and will cause polio and paralysis on an advanced level.
In 1948, microbiologists John F. Enders, Thomas Weller, and Frederick Robbins were trying to find a method to grow different viruses in cell cultures.
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.
The inability to culture polio in non-nerve cells was a major roadblock to developing a polio vaccine.

Eradication targets:

Polio eradication is one of the top priorities of the World Health Organisation (WHO).
Africa was declared polio-free in August 2020; the wild poliovirus has been restricted to rural pockets in Afghanistan and Pakistan.
The WHO’s Global Polio Eradication Initiative is thus set to miss its deadline of eradicating polio by the end of 2024.

Various Polio vaccines:

Salk:

Salk made the first successful vaccine for polio.
It was an Injectable Polio Vaccine (IPV)
Salk inactivated the virus by treating it with formaldehyde, and injected it into his test subjects.
The fragments of the inactivated virus were able to induce immunity in their bodies.
Since the vaccine was introduced into the muscle, it generated systemic immunity.
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.

Sabin:

Albert Sabin developed another vaccine that contained live polio strains weakened by growing them serially in macaque cells, making them unfit for human infection.
This was the oral polio vaccine (OPV).
OPV went into the stomach, it induced a powerful protective mucosal immune response right where the virus would have to begin its infection.

Advantages of OPV over IPV:

The OPV 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.
The OPV was administered orally and didn’t require syringes or trained personnel for its administration.

Challenges in OPV:

The weakened virus in the OPV would revert, and would do the very job it was designed to prevent: cause polio.
The IPV, while being a less potent vaccine, contained inactivated virus particles and carried no risk of causing vaccine-induced polio.
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.