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Polio vaccines

April 24, 2019

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POLIOMYELITIS or polio is a crippling and potentially fatal viral infection which has no cure. Most children with polio do not have any symptoms but contribute significantly to the spread of disease. It is spread through the oral faecal route (food/water contaminated with sewage, or infected people not washing their hands properly), as well as through person to person contact — as the virus continues to be shed from the mouth and nose of the infected individual.

Humans are the only source of the polio virus making global eradication a possibility. In the 1950s a polio vaccine was developed which has been so effective that through the Global Polio Eradication Initiative initiated in 1988, the annual global incidence of polio has dropped by 99.9 per cent, with now only three countries still reporting the disease — Pakistan, Afghanistan and Nigeria.

The sewage waters of Karachi tested positive for the wild polio virus in December 2018, with six cases of children with polio already reported this year. The detection of even a single case of polio anywhere in the world is considered an outbreak. As long as a single child remains infected, all children are at risk of contracting polio.

There are two polio vaccines currently available, 1) Oral polio vaccine which contains the harmless form of the virus, and 2) the inactivated polio vaccine where the virus has been killed. OPV is the preferred vaccine in areas where polio is present to help eradicate disease.

It is a safe, cheap and easy to administer vaccine, which gives better gut immunity than IPV (the primary site for poliovirus multiplication) this intestinal immune response to OPV is probably a reason why mass campaigns with OPV have been shown to stop person-to-person transmission of wild poliovirus.

Children receiving the OPV vaccine also continue to shed the vaccine for four to six weeks after immunisation. This allows ‘passive’ immunisation of people who have not been vaccinated. The more given in outbreak the better the control (the reason for the intensive campaign currently underway). And remember we are already in a global outbreak.

Dr Anokhi Khanum

Karachi

Published in Dawn, April 24th, 2019