A global shortage of inactivated polio vaccine or IPV has hit India too, leaving many children in the country unvaccinated and putting them at risk of contracting vaccine-derived polio. International bodies like the World Health Organisation and UNICEF have been issuing alerts since mid-2016 on shortages after a global switch from an older form of the polio vaccine to the new inactivated polio vaccine.

For the past couple of months, several parts of India have run out of the injectable inactivated polio vaccine. “For the last two months, we have not received any stocks of IPV,” said Dr C Chiplunkar, the official in charge of immunisation in Mumbai. “In most public hospitals, IPV has stopped.”

Serum Institute of India and Sanofi are the only two companies in the world the manufacture the inactivated polio vaccine. UNICEF had originally ordered 111 million doses a year for 2016 and 2017. In May 2016, the two companies could only confirmsupply of about half that amount at 50 million doses for 2016 and 55 million doses for 2017, UNICEF said. In October, WHO officials announced that the manufacturers were having problems producing the vaccine and getting enough raw material of the polio virus.

Scroll.in has sent queries to both the companies but has not received any comment for them yet. The article will be updated once the response is received.

The upshot is that the vaccine is in short supply in many states. Odisha had an injectable polio vaccines stock-out for nearly a month until the government supplied them with the vaccine in February. In Bihar, the immunisation unit has been left with about 2,000 doses of injectable polio vaccines. “It is not being supplied as per the requirement of the state,” said Dr NK Sinha, state immunisation officer for Bihar.

Private hospitals and doctors have been grappling with the shortage for a year now but, in the past few months, stocks in government facilities have started drying up too. Initially, the government had asked private doctors to refer the children to government facilities for IPV but now even government facilities are turning down patients.

“There are several children in my clinic who have not got a single dose of IPV,” said Dr Sameer Sarande, paediatrician from Fortis Hospital in Mumbai. “We can only ask them to wait till the shortage is over.”

India’s universal immunisation programme, in synchrony with the global campaign to end polio, switched from the old polio vaccine that contained live but weakened poliovirus that was administered orally to a combination of oral and injectable vaccines in the second half of April 2016.

The old trivalent oral polio vaccine provided immunity against three types of poliovirus – P1, P2, and P3. However, there was a risk of mutation of the P2 live attenuated virus that could result in polio infection. To avoid this risk, health officials now administer only a bivalent vaccine containing live attenuated P1 and P3 polioviruses orally, along with at least one full dose of the injectable vaccine containing the inactivated poliovirus of all three strains. Along with India, more than 100 countries have introduced injectable inactivated polio vaccines in their immunisation programmes.

Since the switch, the health ministry has recommended that children should be given one full dose of the inactivated polio vaccine at 14 weeks or two fractional doses at six and 14 weeks respectively.

The ministry is now scrambling to make up for the shortage by ordering that only fractional doses of the inactivated polio vaccine be given instead of full doses. Until January, only 16 states in India were administering fractional injectable polio vaccines. “By April, we expect that all states will be administering two fractional doses of IPV at six and 14 weeks,” said Dr Pradeep Haldar, deputy commissioner for immunisation with the health ministry. A fractional dose of injectable polio vaccines is one-fifth of the full dose. “By using fractional doses, all children will get the vaccine despite the shortage.”

The injectable inactivated polio vaccine is licensed globally for intramuscular use. Most vaccines are intramuscular delivered by injection to muscle layers below the skin. Intradermal vaccines, like the rabies vaccine, are delivered to the layers of skin and no deeper. Both routes have different ways of eliciting immune responses.

The health ministry’s plan to offer fractional doses means that the vaccine that was originally manufactured to be injected in the muscle will be administered in the dermal layer. This decision has been based on the WHO’s suggestion that two fractional doses of IPV create a better immune response compared to one full dose.

The injectable polio vaccines is supposed to work on the basis of a priming mechanism. The first full dose or two fractional doses trigger an immune response against the virus. In an outbreak, primed children who have already had these vaccinations are given a booster dose, which significantly improves their immunity against the virus since they have already developed antibodies to it. “A second dose given any time in future will elicit immediate high booster immune response,” said Dr T Jacob John, paediatrician and virologist at Christian Medical College in Vellore, warning that the antibodies created by just one dose are notoriously short-lived.

A child receives polio vaccination drops during a National Pulse Polio Immunisation programme in Amritsar. Credit: Noah Salem/AFP

Fear of vaccine-derived polio

The aim of switching to injectable inactivated polio vaccines is to begin the process of phasing out oral polio vaccines entirely, thus eliminating the risk of vaccine-derived polio from all three strains. However, with many children not receiving the current inactivated polio vaccine now, doctors fear the spread of type 2 vaccine-derived poliovirus especially through sewage systems.

Dr Vipin Vashishtha, senior paediatrician from Uttar Pradesh, said that when the type 2 weakened virus was removed from the oral polio vaccine, there was a sudden gap created in the immunity against type 2, especially in infants born after the switch. “So these kids may be vulnerable to vaccine-derived poliovirus type 2,” he said.

The weakened virus vaccine is also called Sabin vaccine after Dr Albert Sabin who originally developed the vaccine in the 1960s. Sabin 2 is the poliovirus type 2 strain, which is not present in the bivalent vaccine.

“There will be new birth cohorts who had no Sabin 2 and now no IPV due to shortage,” said John. “In case of a vaccine-derived poliovirus 2 appearing in the community, there will be a risk of infection and polio paralysis.”

But doctors are unable to quantify this risk with most saying that there is a “very rare” chance of such an infection occurring. At the same time, Ahmedabad authorities recently detected type 2 vaccine-derived poliovirus in the city’s sewage. In June last year, type 2 vaccine-derived poliovirus was found in Hyderabad’s sewage.

John said that India has 35 vulnerable sites where health authorities are conducting sewage surveillance for the poliovirus. “We hope to detect vaccine-derived poliovirus 2 early enough and intercept before it causes polio in children,” he said.

Rationing is not working

Rationing existing injectable polio vaccines stock into partial doses may not be enough to address the shortage. “Even when we are using fractional doses, there is not enough to meet the demand,” said Dr Hemanta Mishra, the official in charge of immunisation program in Odisha.

Another risk of using a fractional dose is the possibility of a child missing the second dose. “If a child doesn’t turn up for the second fractional dose, what kind of immunity will he have?” asked Dr Raju Shah, senior paediatrician from Gujarat, who also questioned the government’s ability to monitor defaulting patients.

Several doctors also expressed concern that healthcare practitioners and parents of infants were now confused about polio vaccination schedules. In April, only eight states were using fractional doses of injectable polio vaccines. In August, another eight states were asked to use fractional doses and now the entire country is switching to fractional doses. “The government is lucky because parents in our country are not protesting against the shortage,” said Shah.