Eradicating polio

Researchers hope to revise the vaccine strategy for inocculating people in certain parts of the world against the crippling disease polio. Their approach could eradicate this endemic disease once and for all, they report, in this week’s Science magazine.

The new study, by researchers from Imperial College London and
international collaborators explains why the disease continues to afflict people in northern India. Poor sanitation and overcrowded living
conditions in Uttar Pradesh and Bihar pose a dual challenge to the
eradication effort because they encourage poliovirus to spread via infected faeces contaminating drinking water, they explain. This coupled with other infections and diarrhoea interfere with the efficacy of the
oral polio vaccine.

The researchers argue that the simple measure of using a ‘monovalent’
form of the polio vaccine alongside the standard ‘trivalent’ form in
these areas could sufficiently increase the effectiveness of vaccination
programmes to wipe out the poliovirus where it persists.

The trivalent vaccine currently in use contains weakened strains of all
three types of poliovirus, unlike monovalent vaccines, which are
strain-specific. The trivalent vaccine is typically used when more than
one strain of the poliovirus is at large in the population. The problem
with trivalent vaccines is that the three strains can interfere with
each other inside the body, producing immunity to one strain but not
another.

The researchers argue that as the type 1 strain of the virus is now the
dominant one in India, it would be more effective to focus on the
monovalent form of the vaccine.

Lead author Nick Grassly says, “The global polio eradication programme has achieved a great deal. As expected, the last remaining pockets of transmission are the biggest challenge. These pockets of transmission act as sources for all the outbreaks we see around the world today. Our research shows that in northern India the efficacy of the trivalent vaccine is compromised.”

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