Red Alert in Hyderabad
The chance discovery, of a circulating vaccine
derived polio virus (cVDPV), in the murky waters of a sewer in Hyderabad
has figuratively raised a stink. The virus was the P2 strain of the
poliovirus discovered on routine surveillance from 30 areas in the city
on 17 May this year. The entire health machinery was immediately
galvanized into action. The Telangana Government declared a global
emergency. Vaccines were airlifted from Geneva, and more than 300,000
children in the area were vaccinated.
Why is everybody so antsy? Normally when children are
immunized with the oral polio vaccine, the virus replicates in the gut
till some antibodies are developed and is soon excreted in the stool. It
may circulate briefly in the environment infecting a few more children
and eventually die out. However, if an area is seriously underimmunized,
it continues to circulate for extended periods of time. The longer it
circulates, the higher the probablitiy of developing genetic mutations.
And these potentially have the capacity to evolve into strains which can
be paralytic and are termed cVDPV. A circulating VDPV means the virus
has been circulating for at least 12 months in an area which is largely
under-immunized. So, the hullabaloo in Hyderabad seems absolutely
justified. (The Times of India 15 June 2016)
Plant-derived Polio Vaccine
One continues to be awestruck by the ingenuity of the
human mind. A really deep problem looms before us in the final
dénouement of polio eradication. We want to eliminate the use of OPV so
that we mitigate the risks of vaccine-derived polio viral epidemics.
However the IPV has some major limitations. A person vaccinated with IPV
may be completely immune to polio but may get infected with the virus.
He/She then continues to excrete it in the stools; hence allowing the
virus to circulate in the community.
An imaginative solution to this conundrum is
plant-based vaccines. Plant-based vaccines are heat-stable and free from
animal pathogens. They can be genetically engineered to produce proteins
of interest. Usually the antigen and a trans-mucosal carrier protein are
produced by the plant cell. When given orally these proteins are
protected from acids and enzymes in the stomach by the plant cell wall.
On reaching the intestine, gut bacteria release the proteins. The
transmucosal carrier protein transports the antigen across and delivers
it to the circulation and immune system eliciting the required local and
systemic immunity. Scientists in the University of Pennsylvania have
developed a low cost plant vaccine for polio. The gene for viral protein
1 (VP1) which is a structural protein expressed by all polio viruses was
introduced into chloroplasts of tobacco and lettuce leaves. The freeze
dried plant material which expressed the protein was given orally to
mice already primed with an IPV vaccine. High levels of mucosal and
systemic immunity were induced in the mice. The researchers hope to go
ahead with human clinical trials next.
The strategy to use a plant-based vaccine as an oral
booster in place of the OPV has many advantages. Low cost, no
requirement of a stringent cold chain, and no fears of vaccine-derived
mutant polio viruses. (Plant Biotechnol J. 2016;doi:10.1111/pbi.12575)
Africa is Polio-free for 2 Years
In July this year, Nigeria celebrated two years
without a single case of polio. If this continues another year, Africa
will be declared polio-free by next year. Only Afghanistan and Pakistan
continue to report a few cases still. In 2003, few Muslim clerics banned
the use of polio vaccines. Rumors spread like wildfire that the vaccines
had HIV virus and were being used to sterilize muslim girls. As recently
as 2012, Nigeria was reporting half the global cases of Polio. Some
Northern States had imposed a ban on the vaccine. Immunization teams
were attacked after rumors of of vaccine safety. In Northeast Nigeria,
where the militant Boko Haram group disrupted vaccination campaigns,
temporary ‘health camps’ were established offering a range of health
services in addition to the polio vaccine. The continued political
support and will has managed to stem the disease. The polio surveillance
networks were also exceedingly useful in monitoring and controlling the
Ebola outbreak in the last 2 years. So successes in one area spilt over
to the entire health system. Fighting polio has taught us many lessons
well beyond the narrow confines of just one disease. (The Guardian 24
July 2016).
