Polio in Haiti Linked to Incomplete Vaccination
They said World Health officials need to get to work vaccinating children against polio, which is virtually eradicated in most parts of the world.
"The outbreak probably began in Haiti, when a routine oral poliovirus vaccine dose was given to a child living in a community with low vaccine coverage," the researchers, led by Olen Kew of the U.S. Centers for Disease Control and Prevention, wrote in their report.
One of those who died was a 12-year-old boy and another was a boy just 35 months old. "He didn't see his third birthday," Kew said. "If they had only used the vaccine appropriately, this would not have happened."
Two factors are to blame for the outbreak, the researchers wrote in this week's issue of **** The Journal Science ****. One is the low vaccination rate in Haiti and the Dominican Republic, which share an island in the Caribbean.
"Low population immunity was the key risk factor," Kew said in a telephone interview.
"In Haiti, reported coverage rates for three doses of oral poliovirus vaccine for children under one year of age were the lowest in the Americas, falling to around 30 percent nationwide from 1992 to 1997 and remaining below 60 percent by 2000," the researchers wrote.
In the affected Dominican Republic communities only between 20 and 30 percent of people were vaccinated.
The World Health Organization wants to eradicate polio globally, but says the effort has been hampered by a lack of funds and political will in the affected countries. In the United States, polio killed thousands of people and disabled tens of thousands before it was wiped out in 1979.
In Haiti, political strife and poverty have interfered with vaccination efforts, Kew said.
The second factor was the use of an oral vaccine, which uses a live but weakened strain of the virus. The oral vaccine, developed by Albert Sabin, helped rid many countries of polio, including the United States, because it is so easy to give and is highly effective.
But the virus used in the vaccine is still alive, although it has been altered so it does not cause disease.
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It stays alive in the body, and it turns out, it can hook up with other, related viruses called enteroviruses. They swap DNA and the polio virus can become deadly and highly infectious again. It is shed in the feces and gets into the water supply.
People get polio from infected water, so when sewage gets into drinking or washing supplies, the newly energized polio virus can infect them with crippling effects.
Kew said the study shows the importance of getting everyone vaccinated, as the few vaccinated children were, in essence, infecting everyone else.
"Even in developed countries, when people don't vaccinate their kids, the virus can find them," Kew said.
Most people infected with polio have no symptoms. But in a small percentage of cases, the virus attacks the nerves -- usually the spinal cord -- and can paralyze the victim. Between two to five percent of children with paralytic polio die and up to 30 percent of adults.
Humans are the only animals that can be infected with polio, so health officials think vaccination can wipe it out, like smallpox was eliminated in 1978.
There is another vaccine, the inactivated poliovirus vaccine based on one invented by Jonas Salk. This injected vaccination is now widely used because the virus is killed and cannot become dangerous again.
But people who receive the injected vaccine can become infected with wild polio and, while they do not become sick, can spread it.
Kew and colleagues noted that outbreaks of polio have been traced to the oral vaccine not only in Haiti and the Dominican Republic, but in the Philippines and Egypt.
But they stressed that the oral vaccine is still useful, not least because it works better.
"We don't want people to jump to the conclusion that inactivated polio vaccine (the injected version) is the answer," Kew said. 21-22-39.H23