Maulshree Seth
Indian Express
04/16/2010
In a significant study which may force India and a few other countries to change polio eradication strategy, experts from Britain, India and the WHO have found that even vaccinated children in India play a role in transmitting wild polio virus.
So far, health agencies — including Global polio eradication initiative — had been advocating the use of Oral Polio Vaccine (OPV) instead of the inactivated vaccine. The OPV was believed to induce gut immunity ¿ meaning a vaccinated child does not excrete the virus, through which the disease spreads.
But the study — conducted by experts from the Imperial College London, National Polio Surveillance Project, and Global Polio Eradication Initiative, project of WHO — points at the potential of OPV-vaccinated children in transmission of wild virus as well.
The study was conducted on around 14,000 stool samples collected between 2003 and 2008 from healthy children in contact with suspected cases of acute flaccid paralysis, mostly in UP and Bihar. Wild poliovirus was isolated from around 12 per cent of healthy children in direct contact with confirmed polio cases.
The study concluded: “Although OPV is protective against infection with poliovirus, the majority of healthy contacts who excreted wild-type poliovirus were well vaccinated¿ It is clear that OPV is protective against asymptomatic infection with wild poliovirus in India, but that this protection is incomplete.”
The study, called “Asymptomatic Wild-Type Poliovirus Infection in India among Children with Previous Oral Poliovirus Vaccination” has been recently published in the electronic version of Journal of Infectious Diseases, whose printed version is expected on May 15.
Four countries including India, Afghanistan, Pakistan and Nigeria are reporting persistent poliovirus transmission despite various efforts and experts have admitted that Northern India is a unique case in eradication efforts.
Dr VM Vashishtha, the convenor of the Polio Eradication Committee of the Indian Academy of Pediatrics, said: “It is clear now that immunity provided with OPV is imperfect even in case of herd immunity concept, for which OPV was advocated. All we suggest is, if by the end of this year, persistent transmission continues, we should be ready with a Plan B because we cannot allow things to go on.”
In an e-mail, Dr Hamid Jafari, an investigator of the study and Project Manager of National Polio Surveillance Programme of India did not agree that there is an urgent need to change the focus of India’s vaccination programme. “Well vaccinated children (6 or more OPV doses) in close contact with confirmed polio cases, were much less likely to get infected with wild poliovirus compared to the under-vaccinated (0-2 doses),” he wrote , indicating that repeated vaccination with OPV still needs to be undertaken.
Four countries including India, Afghanistan, Pakistan and Nigeria are reporting persistent poliovirus transmission despite various efforts and experts have admitted that Northern India is a unique case in eradication efforts.
Dr VM Vashishtha, the convenor of the Polio Eradication Committee of the Indian Academy of Pediatrics, said: “It is clear now that immunity provided with OPV is imperfect even in case of herd immunity concept, for which OPV was advocated. All we suggest is, if by the end of this year, persistent transmission continues, we should be ready with a Plan B because we cannot allow things to go on.”
In an e-mail, Dr Hamid Jafari, an investigator of the study and Project Manager of National Polio Surveillance Programme of India did not agree that there is an urgent need to change the focus of India’s vaccination programme. “Well vaccinated children (6 or more OPV doses) in close contact with confirmed polio cases, were much less likely to get infected with wild poliovirus compared to the under-vaccinated (0-2 doses),” he wrote , indicating that repeated vaccination with OPV still needs to be undertaken.