India’s immunization Program: How is IPV different from OPV?

Before we proceed to understand how IPV works, let us first explore the concept of vaccination?

 

The basic principle behind the vaccination/immunization is that the pathogen is introduced into the body either in the live attenuated/killed form, to generate memory cells. <Why and How of this will be explored in a short while>

A vaccine will generate a primary immune response which helps in establishing the memory about the foreign antigen. This is what principally happens in the body, when a vaccine is provided into the body.

Now, what will happen when actual virus attacks the body?
There will be a strong secondary <mind it, primary response was seen during vaccination> immune response quickly, which will involve the massive production of antibodies against the same infection.

Now, let’s analyse the difference between primary and secondary immune response?
The primary immune response is weak in potency and work for short duration, where as secondary immune response generates large concentration of antibodies in short duration. The latter helps in providing strength and these antibodies circulate for the longer period of time, mitigating foreign antigens.

Live Attenuated vis-a-vis Inactivated Vaccine
In live attenuated (meaning weakened), the virus which is introduced in the body is not dead, it is only weakened. This virus shows more properties of a real polio virus, which will lead to vaccinated individual developing more memory of polio virus and handling it.

Inactivated vaccines is produced by killing the disease-causing microbe with chemicals, heat, or radiation. Such vaccines are more stable and safer than live attenuated vaccines. The dead microbes can’t mutate back to their disease-causing state.

Now, we come to explore the Vaccine Derived Virus
Actual discussion starts here, because this will showcase the need to introduce IPV for Polio.

One of the disadvantage of live attenuated vaccination is that the safety margins are little less, i.e. if a person is suffering from any serious ailment such as TB, HIV,etc., then his immune system is vulnerable, which might lead to multiplication and mutation of vaccine virus. This will cause clinical infection, which is also called vaccine derived infection.

Now, it will be easy for you to understand the debate on OPV vs. IPV – How is IPV different from OPV?

Injectable Polio Vaccine is made up of heat-killed virus that cannot cause the disease in any case, because the pathogen is not alive. However, it does produce the memory in the cells, required for immunity.

Oral Polio Vaccine is made up of live-attenuated virus, which is nearly incapable of producing an infection.  This type of vaccination helps in providing immunity to wild-type of virus.

Now, what exactly India is planning to do?

  1. National Technical Advisory Group on Immunisation (NTAGI) recommended that India should introduce Injectable vaccine, as we have achieved polio free status.<wild type infection only>
  2. India is introducing IPV in its Universal Immunization Programme (UIP).
  3. There will be shift from tri-valent variety OPV(P1, P2 and P3) to bivalent OPV (P1 and P3), so as to reduce incidence of vaccine-derived poliovirus.
  4. However, IPV will be administered for all the 3 strains of virus, providing immunity to a child from all 3 strains.
  5. IPV will be given in addition to existing OPV, in order to boost population immunity.

Now, the obvious question that arises, that why are we stopping OPV for P2 type?

The wild-type P2 variant was eliminated in 1999. As, it will not be administered in OPV form, the propensity to manifest as a vaccine derived infection will be countered.<In simple words, we will be able to eliminate vaccine derived polio virus of P2 type>

If OPV can lead to vaccine-derived polio infection, then why don’t we switch to IPV only regimen? Because my friend, there are huge challenges in administering IPV:

  • It requires skilled professional, as the vaccine needs to be injected
  • The dosage is very costly, approx $1/dose!

Any further questions?


 

Published with inputs from Pushpendra
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