The detection of type 2 polio vaccine virus from sewage samples in Ahmedabad collected in October and November has exposed lapses in the country’s polio prevention programme. Though the surveillance system in the state was quick to identify the presence of the vaccine virus, the discovery is worrying as children in the neighbourhood may be now vulnerable to vaccine-associated paralytic poliomyelitis.

There is a “rare possibility” of the type 2 vaccine virus transforming into vaccine-derived polio virus which is known to cause paralysis in adults and children, said doctors. Dr Pradeep Haldar, deputy commissioner for immunisation with the Ministry of Health and Family Welfare admitted to the possibility that in the coming nine to ten months, the type 2 oral polio vaccine virus can transform into vaccine-derived polio virus that can infect vulnerable children in the Ahmedabad neighbourhood.

The type 2 polio vaccine virus found in the sewage sample is the attenuated or weakened virus that was used for making the trivalent oral polio vaccine, which was discontinued in April 2016 by the government as a part of the polio “end-game strategy” devised by the World Health Organisation. The strategy involved switching from the trivalent vaccine to a bivalent vaccine effective against the type 1 and type 3 strain of the polio virus. The trivalent vaccine is used to build immunity against both these and the type 2 strain.

The government, the WHO, non-profit health organisations and the medical community in general had worked to create awareness about the switch away from the trivalent oral polio vaccine.

Finding type 2 polio virus in the environment indicates that, despite these efforts, some doctors are still administering the discontinued vaccine to children, said Haldar, whose team screened more than 6,000 healthcare facilities in Ahmendabad in December. They found 40 vials of the trivalent vaccine with local doctors. “Many of them were quacks who were administering the trivalent oral polio vaccine to children despite government stopping its use on April 25,” said Haldar.

Polio programme officials expecetd tot find type 2 vaccine virus in the sewage samples until September 2016 because children continue to shed the vaccine virus in their excreta for some months after veing vaccinated. “We were not expecting to get type 2 vaccine virus in sewage testing in October,” said Haldar. “So we repeated testing in November and concluded that the discontinued vaccine is still being used.”

During the vaccine switching process in April, private doctors in possession of the trivalent oral polio vaccine were asked to exchange the discontinued vaccine for the bivalent oral polio vaccine doses.

Dr Raju Shah, a paediatrician in Gujarat and former president of Indian Academy of Paedeiatrics, said that it was unlikely that doctors are unaware of the switch. “This is just an assumption that the vaccine virus entered the environment because some doctors are still using the vaccine.”

Shah pointed out that there is a possibility that the trivalent vaccine was not discarded properly. “if it was thrown with other waste, it will end up in sewage,” he suggested.

The rare side effects

There is no known cure for polio and the disease can only be prevented with vaccination given multiple times. The infectious disease attacks the nervous system and results in paralysis. Until April 2016, children in India were administered trivalent oral polio vaccine with the live attenuated virus as a part of the national programme to eradicate polio. Since the end of April, with the discontinuation of the trivalent oral polio vaccine, children are to be given the bivalent oral polio vaccine along with the inactivated polio vaccine.

These oral polio vaccines are largely effective in preventing polio. The WHO states that there are only very rare adverse events associated with the oral polio vaccine, which is when a vaccine recipient develops vaccine-associated paralytic poliomyelitis – a risk of one case per 2.4 million administered doses.

Even though the type 2 vaccine virus has been detected in Ahmedabad’s sewage, Gujarat’s official in-charge of immunisation Dr Prakash Waghela said “there is no danger at all” to the health of children.

Doctors say that if the live attenuated vaccine virus infects children and mutates in the guts of children with immunodeficiencies, it can revert to a form that can cause paralysis.

Shortage of inactivated virus vaccines

There has been no transmission of the wild poliovirus in India since January 2011 and the country was certified polio-free by World Health Organisation in 2014. However, India has reported cases of infection by the vaccine-derived polio virus mostly of the type 2 strain. In the absence of vaccination against the type 2 strain, doctors are worried about a “sudden spurt” of type 2 vaccine-derived polio virus cases.

In 1999, the last case of type 2 wild polio virus was recorded in India. “After that there were no cases globally and we don’t want to vaccinate children against the virus which is not in circulation,” explained Haldar.

Another reason for the World Health Organisation to recommend the switching from the trivalent vaccine to the bivalent vaccine to eliminate the risk of paralysis sometimes triggered by the type 2 vaccine-derived polio virus.

The bivalent oral polio vaccine is administered in combination with an inactivated polio virus vaccine. “This situation would have not been a concern, if the trivalent vaccine was still in circulation,” said Dr Nidhi Bhatnagar, assistant professor at the department of community medicine at the Army College of Medical Sciences from New Delhi.

Children who have been vaccinated with oral polio vaccine shed the virus in their excreta. The presence of the type 2 polio virus in sewage puts children, especially those with low immunity living in the vicinity of such sewage, at risk of picking up the virus through the fecal-oral route and contracting polio.

Bhatnagar explained the vulnerability of children who have not received the inactivated polio vaccine. “These children don’t have immunity against type 2 strain,” she said. “They can suffer from vaccine-associated paralytic poliomyelitis.”

Since April, one intra-muscular dose of inactivated polio vaccine at 14 weeks or two intradermal fractional doses at six and 14 weeks should be given to children. “The shortage is so severe that some children are not even getting one dose of the inactivated vaccine,” said Shah.

Haldar said that while there was a global shortage, India has enough stocks to meet its requirements.

Not the first time

About 809 cases of paralysis due to vaccine-derived polio virus were reported globally since the year 2000. The emergence of vaccine-derived polio virus does not jeopardise the “polio free” status of the country.

In July, Hyderabad’s health authorities inoculated close to three lakh children after type 2 vaccine-derived polio virus was found in sewage samples. Haldar said that in Hyderabad, the decision of vaccinating children was taken to protect them from developing vaccine-associated paralytic poliomyelitis.

According to the World Health Organisation, a five-year-old boy from Siwan district in Bihar was detected with vaccine-derived poliovirus type 2 in April. He had developed paralysis in February and the health officials were screening the area for any vaccine-derived polio virus strain circulating in the neighbourhood where he lived.

Bhatnagar explained the phenomenon. “If the vaccine virus is in the environment which is conducive, it can replicate and mutate to become a vaccine-derived polio virus which can cause the disease in children especially those who have no immunity against type 2 polio virus,” she said.

“In Ahmedabad, we are dealing with the vaccine virus and there is no need to inoculate children living in the vicinity,” said Waghela. He is of the view that the vaccine virus that has not mutated into a vaccine-derived virus cannot cause disease at the moment, which is why the department is not undertaking inoculation drives like those carried out in Hyderabad.