What is IPV (Inactivated Polio Vaccine)?

An extremely virulent and dangerous condition, polio was once a global killer that, when not fatal, could cause lifelong debilitating paralysis. Thanks to over 4 decades of vaccination, polio is no longer as widespread or as feared as it once was, and this is due to the use of polio vaccines across the world. In this article we look at one particular type of polio vaccine, the IPV (inactivated polio vaccine), and how it is used to immunise against this dangerous disease.

History of IPV

The IPV was first developed in 1952, although many years of testing meant that its use was not truly established until much later. The vaccine was developed by its namesake, Jonas Salk, and is often referred to as the Salk Vaccine. This vaccine is actually a mixture of three strains of poliovirus all of which are grown inside a specially designed tissue culture systems. These viruses are grown and then killed before being prepared for human administration.

The Salk Vaccine or IPV has undergone some changes over the years, but in essence and principle it remains more or less the same. As technologies have improved the manufacturing process has been refined, and the vaccine is now safer and more effective than ever. IPV is manufactured and distributed across the world as part of national vaccination schemes and global vaccination initiatives. The development of IPV was very much the first step towards the elimination of polio, which can now be considered a real prospect in the years to come.

How does IPV work?

The IPV is part of a class of vaccines known as inactivated vaccinations. These are composed of dead pathogens injected into the body induce an immune response. Because they have been specially treated, these pathogens, in this case the poliovirus, are perfectly safe as they do not actively work against the body and induce disease. However despite this, they still possess the characteristics which indicate the fact that they are invading pathogens to your body’s defences, making them a great way of safely inducing an immune response.

More specifically the Salk Vaccine works by stimulating a particular segment of the immune system. Your body’s defences are a complex network with many different response elements, and by triggering parts of that immune system, which then learn how to respond more effectively to an infection, vaccinations induce immunity. The Salk Vaccine provides what is called IgG-mediated immunity, which means that the vaccine stimulates the production of IgG (immunoglobulin G) antibodies. These are small molecules that recognise poliovirus and adhere to it, either inactivating the virus or marking it for disposal through other mechanisms. Once IgG production has been stimulated by the vaccine, your body will keep a reserve of that particular antibody to defend against any future infections.

All in all this system is very effective, and the best evidence for that is the massive decline in incidences of polio across the world. However a major caveat of inactivated vaccination is the fact that multiple doses need to be supplied for lasting immunisation. These are called booster doses, and they top up the quantities of IgG in our blood. If a person misses their booster dose of the vaccine, then they are no longer adequately protected against potential polio infections.

When is IPV given in the UK?

Polio is given at a number of different key points in the childhood vaccination programme. It is usually administered as part of combination injections that also protect against other conditions to spare infants the discomfort of multiple injections.

At 2 months the DTaP/IPV/Hib injection is administered, an injection also referred to as the 5-in-1 which immunises against Haemophilus influenzae B, diphtheria, tetanus, and whooping cough as well as polio. The booster doses of this vaccine are given at 3 and 4 months of age and, as mentioned in the previous section, are needed to ensure that a child is adequately protected against any potential polio infection. 

At about 3 years  and 4 months of age (before they go to pre-school) children in the UK are given another booster against polio through the DTaP/IPV injection, also known as the 4-in-1. Once in pre-school children are exposed to a wide range of new pathogens that can thrive on a population that hasn’t been immunised.

The final IPV injection is a teenage booster given between 13 and 18 years of age. This injection immunises is a 3-in-1 which is often organised by schools.

Why is IPV used rather than the oral polio vaccine?    

An alternative to IPV is the oral vaccine. This is a live attenuated vaccine rather than an inactivated strain, and the difference is that the former contains living (albeit weakened) poliovirus. The oral vaccine is very effective and immunises after as little as a single dose, and while it was at one point an integral part of the global vaccination initiative, it is no longer used as broadly.

While effective, live vaccines do carry some risks. They can’t be safely used on pregnant women or people suffering from any kind of immune problem. They also carry with them a slight risk of reversion, which means that the normally safe attenuated virus can potentially undergo a genetic change that transforms it into a highly virulent version of the disease. While in the past these risks were acceptable because of the benefits the oral vaccine offered, polio is no longer as much of a threat, and as such immunisation programmes use the safer IPV.

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