21 Apr 2016

Which type of polio vaccine is best?

By Dr Jodie Abramovitch

The current polio vaccine was developed by Albert Sabin in 1961 and is a live-attenuated, orally administered vaccine (OPV). Live-attenuated means that the polio virus is alive but unable to cause disease. In settings with high childhood mortality, the OPV is believed to have non-specific effects that allows for protection against other childhood infections such as paralytic poliomyelitis (also known as infantile paralysis caused by the polio virus), tuberculosis and measles. This non-specific protection is thought to be able to reduce mortality to infectious diseases, particularly in childhood, by up to 17%. The significance of this protection is controversial.
Professor Magda Plebanski
To reduce the incidence of poliomyelitis which is around 75 cases worldwide per year, the World Health Organisation (WHO) has recommended the OPV be replaced by an inactivated form (IPV) of the polio virus. Inactivated means the virus used in the vaccine is dead.

In a recent correspondence published in The Lancet, a group of physicians and scientists, including Professor Magdalena Plebanski from the Department of Immunology and Pathology, voiced their concern at a potential change to the form of the current polio vaccine from OPV to IPV. It was noted that previous evidence suggests that the IPV does not confer the same non-specific protection as the OPV. Therefore, the IPV may be associated with an increase in childhood mortality (caused by a range of different infectious diseases). The authors postulated that for every case of poliomyelitis that is reduced by the IPV about 4000 extra deaths due to other infectious diseases (resulting in 300 000 additional deaths each year) may occur that could have been prevented by the OPV.

The authors of this correspondence concluded by urging the WHO to conduct randomised trials of the two different forms of polio vaccine before phasing out the OPV. This would allow for a better understanding of the non-specific protection that each of the polio vaccines provides against other infectious diseases. The results of these trials would inform whether the IPV leads to a higher infectious disease mortality overall when compared to the OPV, as well as whether the OPV and IPV may be administered alongside one another in children to prevent poliomyelitis and keep infectious disease mortality low.

Reference: Fish ENFlanagan KLFurman DKlein SLKollmann TRJeppesen DLLevy OMarchant ANamachivayam SNetea MGPlebanski M,Rowland-Jones SLSelin LKShann FWhittle HC.  Changing oral vaccine to inactivated polio vaccine might increase mortality. Lancet. 2016 Mar; 387:1054-5.
doi: 10.1016/S0140-6736(16)00661-9.

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