Vaccine used to combat polio causing infections

Vaccine used to combat polio causing infections

Chennai,  Jan 2016: 

The country completed five polio-free years on Wednesday, but it still faces a hurdle that virologists had been warning about all these years the very vaccine used to fight polio is causing infection in some children.

In 2015, two children, including a two-year-old child from New Delhi, tested positive for vaccine derived polio virus (VDPV). So far, 44 cases of VDPV have been reported in India. The King Institute of Preventive Medicine in Chennai, one of the eight WHO-authorized laboratories for polio in India, did not see any case. In the past one year, it tested 10,559 stool samples in patients with polio-like symptoms after taking oral drops. Vaccine-virus was detected in 151 stool samples tested in the laboratory.

"This is not unexpected. As part of the mass immunization programme, we give oral polio drops to children below five. This vaccine has live attenuated virus. Some children may develop polio-like symptoms but like everyone else the virus will be flushed out of the person's system within three months," said institute director Dr Gunasekaran.

Oral polio vaccine (OPV) contains a weakened vaccine-virus, activating an immune response in the body. When a child is immunized with OPV, the weakened vaccine-virus replicates in the intestine for a limited period, developing immunity by building up antibodies. On rare occasions, if a population is seriously under-immunized, an excreted vaccine-virus can continue to circulate for an extended period. "The longer it survives, the more genetic changes it will undergo," Former Public Health Director Dr S Elango said. In very rare instances, the vaccine-virus can genetically change into a form that can cause paralysis, he said. "Every child who has tested positive for the virus in the stool should be followed up and monitored every month by a health worker," he said.

While there has always been a debate on the safety of OPV compared to injectable polio vaccine, Dr Henk Bekedam, WHO representative to India, said as a long- term measure, to prevent VDPVs, oral polio vaccine should be gradually withdrawn from the programme after wild poliovirus has been eradicated. As part of the global polio endgame plan, the health ministry is preparing for withdrawal of type 2 component of OPV in April 2016. "This will ensure no VDPV occurs due to type 2 that cause most VDPVs globally," he told TOI.

Director of Public Health, Dr K Kolandaisamy said there was no cause for worry if a child tests positive for virus in stools during AFP surveillance as in areas of inadequate sanitation, this excreted vaccine-virus can spread in the immediate community and offer protection to other children through 'passive' immunization, before eventually dying out. "However, we will continue to immunize children until we eradicate every VDPV case," he said. Pharma Times