Scores of health workers from within India and abroad will be monitoring what is being billed as the largest ever mass vaccination drive with Inactivated Polio Vaccine (IPV), ever since a polio virus strain was detected from a sewage sample near the Secunderabad railway station in Telangana. For the State’s health authorities, the injectable vaccine is now its weapon to tackle any chances, however remote, of polio infection.
The polio find in Telangana made headlines when sewage samples drawn from four locations in Hyderabad by Telangana’s Institute of Preventive Medicine in May this year, as part of a World Health Organization (WHO)-mandated polio surveillance programme, were tested at the Indian Council of Medical Research’s Enterovirus Research Centre in Mumbai. One sample, from a sewage treatment plant in Amberpet, and a densely-packed locale considered to be a high-risk pocket in Hyderabad by the health administration, showed the presence of type-2 vaccine-derived polio virus. Genetic analysis at the institute also showed the virus had undergone 10-nucleotide changes.
‘No cause for alarm’ “If the weakened type-2 virus used in oral polio vaccine [OPV] continues to multiply for long, mutations may arise. If there are six or more nucleotide changes in the type-2 weakened virus then it is called vaccine-derived poliovirus (VDVP). There have been 45 cases of vaccine-derived poliovirus human infections since 2009. Most have been cases of isolated infections. There have also been numerous instances of the virus being found in the environment as part of our surveillance,” said Dr. Pradeep Haldar, Deputy Commissioner – Immunisation, Ministry of Health and Family Welfare, adding that the last find of the virus in the environment was in New Delhi earlier this year. “The risk of human infection is low in Hyderabad and there is no cause for concern.”
At the behest of WHO, Central and State health authorities did a quick survey of 2,000 households in the vicinity of the Amberpet plant. to assess the robustness of country's polio surveillance network. They found no missed cases of Acute Flaccid Paralysis, where there is the classic symptom of Poliomyelitis disease caused by the virus when it attacks the nerve cells in spinal cord, leading to irreversible muscle wasting. The exercise also revealed that over 94 per cent of the children were immunised with at least three doses of trivalent oral polio vaccine (tOPV), a finding consistent with claims made by the State government following the national polio immunisation programme carried out in February this year. A single-dose mass IPV vaccination campaign was the selected response.
“Our response this time has garnered attention due to vaccine availability and given that we decided to use IPV,” Dr. Haldar said. Trivalent OPV administered in India until April 24 this year contained live but weakened type 1, 2 and 3 polio virus. Subsequently, the country switched to bivalent oral polio vaccine or bOPV by dropping type 2 as this variant was responsible for vaccine-derived polio cases. Concomitantly, the injectable IPV was introduced, containing killed viruses of all three types; viral-shedding is a non-issue with IPV.
Intra-dermal administration Observers from the Centers for Disease Control and Prevention, U.S., along with health representatives from Nigeria, where until recently polio was considered endemic, are expected to be observe the vaccination campaign. The Health Ministry has also mobilised IPV stock from the Government Medical Store Depot in Chennai at a time when it is scarce in public health institutions and unavailable with private sector. The vaccination drive is scheduled to start from June 20 but shortage is on top of the mind. “Though equally effective, vaccine is being administered intra-dermal when it is normally administered intra-muscular. Giving it in the skin reduces the dose quantity by a fifth but requires some skill on the part of health professionals administering it,” said Dr. G Srinivasa Rao, Chief Programme Officer, National Health Mission, Telangana.
Before efforts to eradicate the virus began in the 1980s, polio affected hundreds of children every day, mainly spreading by the faecal-oral route. To this day, under-immunised and immune-compromised individuals are considered a risk as they tend to shed the virus in their stool for extended periods of time, thus warranting a gradual shift to IPV. The polio vaccination drive from Monday is a Herculean task in ensuring that every child receives a shot without conventional door-to-door campaigning, A 2014 paper published in the journal Science reported that IPV, when given to children who have been vaccinated with OPV, boosted gut immunity and reduced intestinal shedding of the virus. Gut immunity, imparted mainly by OPV, is among the prime arguments for continuing with the oral vaccine in the developing world despite the risk of viral shedding in unhygienic environs. The health administration is confident its surveillance network is robust and that it can mount a rapid vaccination response for the world to see and learn from.
rohit.ps@thehindu.co.in
