Polio cases linked to heat-affected vaccines

KARACHI, Oct 24: Health authorities in Sindh have expressed doubts about the efficacy of polio vaccines provided by the World Health Organisation for use during immunisation campaigns against the dreaded disease, which has affected 27 children in Sindh so far this year, it emerged on Monday
Reports say that the OPV with a late stage VVM (indicating that a vaccine has been exposed to heat for long) have also been used during campaigns due to inconsistent cold chains, low-level education of workers or for other reasons
According to experts, each vial of OPV has a VVM having four stages that indicate if the vaccine has been exposed to heat, which can make it ineffective. The VVM comes in stage one, which remains constant as long as the vaccine is not exposed to heat. With continued exposure to heat, the VVM moves to stages two, three and finally to stage four.
The health high-ups wanted that polio vaccines with VVM stage 2 should not be supplied to the towns and talukas as it might move to stage 3 or 4 when used.so the WHO had been asked to provide zero-VVM vaccines to prevent them to move to stage 3 or 4.
Experts maintained that there was a margin of safety built into the VVM so that even a late stage VVM might be potent, but the vaccine had had enough exposure to heat that it should be discarded because it was potentially weakened. Using a vaccine with a late-stage VVM is not harmful, but it might not offer immunity.
The provincial director for the expanded programme on immunisation, Dr Mazhar Khamesani, said the three-day campaign, which could not take off on Oct 24, would be launched on Oct 25. During the campaigns about 21,000 teams of vaccinators and volunteers would administered OPV to about 6.5 million children aged up to five years, he said, adding that parents of children aged from six months to five years should also ask the teams to give vitamin A doses to the children as well