Polio outbreak in Yemen keeps growing By Donald G. McNeil Jr. The New York Times
THURSDAY, MAY 12, 2005
NEW YORK More than 40 new cases of polio have been confirmed in Yemen, the World Health Organization said, more new cases than in any other nation.
"It's a much bigger outbreak than we originally thought, and it's spread throughout the country," Dr. David Heymann, who is in charge of the WHO's polio-eradication campaign, said Tuesday.
Epidemiologists expect the 63 cases confirmed so far in Yemen to grow to more than 100 soon. It takes about six weeks to test stool samples from each paralyzed child to confirm infection. Nigeria, previously the worst-hit country, has confirmed 54 cases this year.
Yemen was already planning to vaccinate its five million children younger than 5, Heymann said. Six million doses of a new type of vaccine that should immunize more efficiently are being shipped, he said.
The new, monovalent vaccine contains a weakened strain of Type 1 polio virus only. The old, trivalent vaccine also contains strains against Types 2 and 3. But only Type 1 virus exists in Yemen, while the vaccine against Type 2 tends to beat its rivals to the receptors in the gut and block them, so six to eight doses of trivalent vaccine may be needed to get good immunity against Type 1 polio.
The monovalent vaccine appears to create immunity with a single dose about 65 percent of the time, Heymann said. Yemen's misfortune carries with it the benefit of "permitting us to try out this new strategy," he said.
Monovalent vaccine was first used in India last month, and will be in Indonesia and Egypt soon, he said. Type 3 polio still exists in Nigeria and in an Indian state, so monovalent cannot be used in those areas. Type 2 polio was eradicated six years ago.
The first cases of polio in Yemen since 1999 - four children in Al Hudaida, a Red Sea port - were confirmed on April 21. Genetic testing showed they were infected with a strain that originated in northern Nigeria. In 2004, Nigeria had the world's worst record, with 792 new cases, followed by India with 136 and Sudan with 127.
