You may have often heard the term “OPV” or “OPV Vaccine” being used in the context of babies’ health, without knowing what it meant. OPV is short for Oral Polio Vaccine.
What is OPV?
As is evident from the name itself, OPV is a vaccine that is administered to prevent contracting Poliomyelitis. It is administered to babies when they are very young, starting from birth (zero dose) and then 3-4 consecutive doses starting as early as 6 weeks.
There are two types of vaccines for polio. One is injected into the body and consists of inactivated poliovirus; this is IPV or Inactivated Polio Vaccine. OPV, however, is orally administered and consists of weakened strains of poliovirus.
Poliovirus has three variations. In lieu of this, there are three types of OPV. They may contain one, a combination of two, or all three strains of the three (weakened) variations of the virus. It works in two ways. Firstly, it produces antibodies for the strains of virus that are present in the OPV, depending on which type of OPV is administered. Secondly, in the case of an infection, it prevents the virus from spreading to the nervous system and also prevents polio paralysis.
The advantages of OPV are:
1. It is less expensive than injections, which makes it more cost effective.
2. It is easy and painless to administer.
3. It is effective and provides long term and long lasting protection.
4. It produces a local, mucosal immune response in the lining of the intestine which prevents the transmission of the virus.
5. The vaccine virus is also excreted in the first few weeks after vaccination while it is multiplying. This can therefore spread to others, leading to “passive immunization.”
The reason that IPV is gaining popularity over OPV is because IPV contains kills strains of the virus. With weakened strains, there is a small (1 in 2.4 million) chance of developing a condition called Vaccine-associated paralytic poliomyelitis, which doesn’t exist with the inactivated virus (IPV) since the virus is killed. This is why it is recommended to also administered a dose of IPV after the 4 doses of OPV have been administered.
Immunization Schedule for OPV
The primary polio vaccination series consists of 3 OPV doses and 1 IPV dose, following the first dose administered at birth. This first dose of OPV administered at birth is known as the zero dose, OPV-0. Following this, the ‘first dose,’ OPV-1, should be administered at 6 weeks old. The following two doses can be administered in intervals of four or more weeks, i.e., OPV-2 should be administered around 10 weeks old and OPV-3 should be administered around 14 weeks old. The minimum interval between doses is 4 weeks. If one dose of IPV is being administered, it should be done at 14 weeks along with the dose of OPV. An additional dose of OPV (booster) can be administered between 16-24 months of age.
It is essential to get the vaccination by 6 months old because children between the age of 6 months and 3 years are the most susceptible to contracting polio.
Why do we still need it in India?
Even though India is now polio-free, it is still essential for these vaccines to continue being administered. The reason for this is because polio is still at large in many other countries of the world, including our neighbouring countries such as Afghanistan and Pakistan. Due to this, India is at high risk of re-entry of polio. In order to make sure that India stays polio-free, it becomes necessary for the vaccine to continue being administered.