April 13, 2024

Understanding the Importance of IPV Vaccines for Protection against Polio

What is Polio?
Polio is a highly infectious viral disease which mainly affects young children. The virus is transmitted person to person, usually through the faecal-oral route or, less frequently, by a common vehicle (for example, contaminated water or food) and multiplies in the intestine. Initial symptoms are fever, fatigue, headache, vomiting, stiffness in the neck, and pain in the limbs. In a small proportion of cases, the virus enters the bloodstream and attacks the central nervous system causing muscle weakness and paralysis. Among those paralyzed, 5%-10% of patients die when their breathing muscles become immobilized.

Types of Polio Viruses
There are three types of wild polio viruses (WPVs), namely WPV1, WPV2 and WPV3. Each type can cause paralysis. WPV2 was eradicated in 1999 and no case of WPV3 has been found since 2012. However, WPV1 remains endemic in only two countries -Pakistan and Afghanistan. Over 90% of polio cases worldwide are caused by WPV1 alone. Apart from wild polio viruses, there are also vaccine-derived polioviruses (VDPVs) which can arise from oral polio vaccine strains circulating in under-immunized populations for a long time. They have genetic and biologic properties virtually indistinguishable from wild poliovirus and can cause paralysis.

How are Polio Viruses Prevented?

The only way to prevent polio is through immunization. The oral polio vaccine (OPV) contains an attenuated (weakened) form of live poliovirus that can replicate in the intestine and induce strong intestinal immunity. The main advantage of OPV is its ability to generate intestinal immunity to stop person-to-person transmission of wild poliovirus. However, rare vaccine-associated paralytic polio (VAPP) can occur from reversion of the attenuated vaccine strains to a virulent form.

The inactivated polio vaccine (IPV) contains an inactivated/killed form of the three poliovirus serotypes that cannot replicate or cause polio. IPV Vaccines  is safer than OPV since it cannot cause VAPP. However, it does not induce intestinal immunity and therefore does not stop person-to-person transmission of wild poliovirus. IPV primarily protects the vaccine recipient from paralysis in case of disease.

Global Polio Eradication Initiative and Role of IPV
In 1988, the World Health Assembly launched the Global Polio Eradication Initiative (GPEI) with the goal of worldwide eradication of wild poliovirus by the year 2000. Excellent progress was made initially with OPV but the initiative faced multiple challenges in the last stages of eradication. Switching to IPV was identified as a key strategy to overcome these challenges.

Some key advantages of IPV include:

IPV cannot cause VAPP or cause outbreaks of circulating vaccine-derived polioviruses like OPV.

IPV can protect communities through vaccination of children and boosting population immunity in areas with silent circulation of wild poliovirus even in the absence of intestinal immunity.

IPV can break the chain of person-to-person transmission of wild poliovirus in the final push towards eradication.

Growing Importance of IPV for Post-Eradication Era
With global polio eradication inches away, the focus is shifting to long term use of IPV to maintain a polio-free world after certification of global eradication of wild poliovirus. Some key reasons for this growing reliance on IPV include:

Continued risk of vaccine-derived polio outbreaks from use of OPV globally. Switching to IPV can eliminate this risk.

Need for countries to be completely free of all polioviruses- both wild and vaccine-derived. IPV is essential to achieve this.

Desire to stop all oral vaccine use and withdrawal of all OPV globally once wild polio is eradicated to secure the endgame of polio eradication.

IPV is considered the long term strategic vaccine for a post-wild polio world that only contains IPV in routine immunization programs globally.

Recent experience of outbreaks from circulating vaccine-derived poliovirus underscores the importance of sustaining high IPV coverage worldwide.

Growing confidence in IPV’s ability to provide protective immunity to all three serotypes of poliovirus without risk of reversion or transmission.

Ensuring High Coverage with IPV
With its greater strategic importance in the endgame and post-eradication era, global coverage with at least four doses of IPV must be enhanced significantly in all countries. This requires:

Adding at least one dose of IPV to national routine immunization schedules, and increasing doses where feasible based ondisease risk.

Introducing IPV into outbreak response immunization activities along with OPV.

Ensuring sustainable supply of quality IPV at affordable prices promoted global access especially in low income countries.

Strengthening communication to convince communities about safety and importance of IPV for long term protection.

As the world nears polio eradication, IPV has emerged as the strategic vaccine to secure a polio-free future globally. High population immunity with IPV through robust routine and supplementary immunization activities is key to eliminate both wild and vaccine-derived polioviruses completely.

1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it