a1253: Polio outbreak in Haiti and DR linked to vaccine (fwd)

[Bob Corbett <corbetre@webster.edu>]

From: Greg Chamberlain <GregChamberlain@compuserve.com>

By Michael Smith

ATLANTA, March 14 (UPI) -- Scientists at the Centers for Disease and
Prevention reported Thursday that for the first time, the oral polio
vaccine has led to an outbreak, not just an isolated case of the disease.
   Twenty-one people were affected by paralysis and two died between July
2000 and July 2001 on the Caribbean island of Hispaniola, which is shared
by Haiti and the Dominican Republic. Eight of the cases, including the two
fatalities, were in Haiti, CDC virologist Olen Kew said.
   Because the oral vaccine contains a live mixture of the three strains of
the polio virus, Kew said, "we had been concerned on theoretical grounds
that (polio) might spread" through the use of the vaccine.
   But until the Hispaniola cases, "there had been no outbreaks from the
process," he said. Kew is the lead author of a paper analyzing the outbreak
published in Science Express, an online extension of the journal Science.
   The first case, reported in the Dominican town of Bonao in July 2000,
took medical officials by surprise, he said, because Hispaniola -- like the
rest of the Americas -- was thought to have eradicated wild polio virus in
1994.
   At first, Kew said, Caribbean scientists thought the Bonao case was a
resurgence of wild polio, but genetic analysis showed the virus involved
was closely related to one of the strains used in the oral vaccine.
   The second case, in Port-de-Paix, Haiti, also involved a virus descended
from the oral vaccine, but with enough differences from the first case that
researchers concluded the disease had been evolving and mutating for at
least a year, Kew said.
   What probably happened, he said, is a child in Haiti was given the oral
vaccine, but neighboring children were not. Some of those children were
infected, and passed the virus on until eventually cases of the illness
came to the notice of medical officials.
   Most polio infections, Kew said, do not result in disease.
   The oral vaccine has been linked to isolated cases of polio in the past,
according to infectious diseases specialist Bill Fong of the University of
Toronto. "The surprising thing is the number of cases and the severity of
disease in this outbreak," he said.
   "It means the strain was upgrading and probably mutating to become more
virulent," he said.
   A global effort to wipe out polio, under the direction of the World
Health Organization, is nearly complete. Unlike the flu virus, for
instance, polio only infects humans; if enough people are immunized,
scientists argue, the virus will die out.
   Kew said the Hispaniola outbreak shows the need to push on with the
eradication effort, but he added the oral vaccine should be phased out in
an orderly manner once polio is wiped out.
   An injected vaccine, which uses killed virus and is regarded as safer,
although more difficult to use, would replace the oral vaccine, he said.