Wednesday, 23 May 2012

Scientists now plan to develop a virus that is partly alive and partly dead to keep the world free of polio cases for ever

Syed Akbar
Hyderabad: City scientists now plan to develop a virus that is
partly alive and partly dead to keep the country free of polio cases
for ever.

The city-based Ella Foundation, which bagged a grant of one lakh US
dollars from Bill and Melinda Gates Foundation, will work on a virus
that is “disabled” but effective enough to prevent new cases of polio
in the country. The highly ‘disabled’ virus, to be developed by the
city team, will ‘check-mate’ polio after the phasing out of oral
poliovirus vaccine.

Viruses are pathogens that can only reproduce inside cells. Ella
Foundation scientists propose to halt one or more of the processes,
which are required for the reproduction of poliovirus inside cells.
What they anticipate is that the virus will reproduce partly and hence
is partly alive but cannot complete its circle of life and is
therefore partly dead.

“We hope that this highly ‘disabled’ virus will mimic live virus to
some extent, tickling the body defenses to an extent beyond what the
killed virus would do,” said Dr Krishna Ella, co-founder, Ella
Foundation. Because the ‘disabled’ virus does not reproduce and hence
cannot spread, it also can not cause vaccine-derived polio.

Polio vaccines are of two types: live but attenuated virus given
through oral drops (OPV), and killed virus vaccine (IPV) given through
injection. The new virus will give the benefits of both oral polio and
injectable polio vaccines.

“Once there are no cases of the disease reported, the live vaccine can
no longer be used because of two reasons. One, the live virus spreads
within the body and can go around in the environment to spread to
other people. Two, in rare cases, it can cause disease – the so called
vaccine-derived polio.  Therefore, the world is moving towards using
killed vaccine,” Dr Krishna said.

However, there are several problems in using a killed vaccine as
compared to a live virus vaccine. The former does not reproduce itself
in the body and hence does not induce all body defences. Secondly,
large doses are needed for killed virus to produce the required
defence mechanisms. The requirement for large doses also takes more
resources to manufacture enough number of doses to cover large
populations. On the other hand, killed virus vaccine is neither
associated with spread within the community nor does it cause disease.

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