On January 18, the Ministry of Health and Family Welfare sent an urgent letter to all states except Bihar, Madhya Pradesh and Kerala saying that it had decided to postpone the polio National Immunisation Day scheduled for February 3 due to “unavoidable circumstances”. The ministry said that it will tell the states when a new date is fixed.
On January 24, the ministry issued a press release denying media reports of a shortages of polio vaccines in the country. The Print had reported earlier in the day that National Immunisation Day had been postponed because of vaccine shortages.
The ministry said that it had already secured the required quantity of bivalent oral polio vaccine or bOPV but it the vaccine was being out through more stringent tests and can only be sent to states for use after each batch has been cleared by a national testing laboratory. The ministry also said that there is not shortage of the inactivated polio vaccine or IPV that has only recently been introduced in India and also dismissed the claim of a shortage of funds to procure that vaccine, despite a steep hike in its price.
However, it is true that the global supply of IPV has been constrained. Gavi, a global vaccine alliance that supports immunisation in low-income countries including India, has acknowledged that the pace and scale at which countries have started using IPV, along with difficulties in scaling up production capacity means that the situation will be fragile until 2020.
Why is a possible polio vaccine shortage such a big threat in India?
India’s largely successful strategy to eradicate polio has been to conduct mass immunisations. National Immunisation Days are held twice a year on which about 172 million children are vaccinated. These mass vaccinations confer herd immunity on the population. This is necessary in India where in many communities, parents do not take their children regularly to the doctor for routine immunisations.
Many states that are at higher risk of polio outbreaks like Uttar Pradesh and Bihar also have sub-National Immunisation Days, supplementing the pan-India immunisation programme.
India’s last wild polio virus infection occurred in 2011. A year later, the WHO removed India from the list of countries with active endemic wild polio transmission and in 2014 declared India polio free. However, this does not mean that there have been no polio cases in the country since then. India still records a number of vaccine-associated polio cases, which cause the same physical symptoms as wild polio. It is to eradicate such vaccine-associated polio paralysis that India is switching from using the OPV to IPV.
The vaccination mechanism
There are three strains of the polio virus – type 1, type 2 and type 3 – all of which were originally wild, naturally occurring viruses that cause infections and paralysis, mostly in children. OPV, which has been widely used around the world to bring polio under control, contains a live but weakened strain of polio virus to trigger an immune response and is administered orally. IPV contains a killed or inactivated polio virus and is administered through injection.
IPV is effective in protecting an individual but does not stop transmission of the virus between people. OPV not only triggers an immune response, it can also wipe wild polio out in the environment by replacing it with the weakened, non-pathogenic form of the virus. This occurs when the vaccine virus is passed through the excreta of immunised children into the environment. Children who pick up the weakened virus from the environment get immunised even if they have not received the vaccine. This is one of the underlying principles of the Pulse Polio campaign in which millions of children are provided the vaccine within a space of days to ensure maximum coverage.
However, OPV carries a risk. Sometimes, the vaccine virus can mutate in the human intestine, regain its virulence and become the vaccine-derived polio virus, which can then spread in the environment. This form of virus can cause polio in children who have not been immunised.
The global strategy for all areas that have eradicated wild polio viruses is to switch from using OPV with live attenuated polio virus to IPV with the killed virus. On April 26, 2016, health authorities around the world implemented a global synchronous switch in which all trivalent oral polio stocks – containing all three strains of the virus – were destroyed to prevent any form of the live type 2 vaccine circulating again. Only a bivalent oral polio vaccine containing the live weakened type 1 and type 3 viruses has been used since then along with the trivalent IPV containing killed strains of all three types of viruses.
It is important to continue to immunise children with OPV until there is enough IPV to vaccinate all children. This is because vaccine-derived polio virus can circulate in the environment for a long time, sometimes even up to two years. Even if OPV is discontinued, there may be silent transmission of the vaccine-derived polio virus in the community. If children who have not been immunised pick up the virus it can lead to widespread outbreaks of the disease that are difficult to contain.
This is why children need to be continuously immunised against polio even though India has been declared polio free. It is also why a shortage of vaccines can seriously endanger children and the progress that India has made over decades in fighting off polio.