Overview of Polio Epidemic in Yemen
Apr 29, 2005 - 7:23:38 PM

Eighteen new cases of polio have today been announced in Yemen, bringing the reported total number associated with an outbreak in the country to 22. Yemen had been polio-free since disease surveillance began in 1996 - a genetic investigation is ongoing to determine the precise origin of the outbreak. Experts fear that the number of cases will rise in the immediate future.

Teams of WHO and Ministry of Health epidemiologists and paediatricians remain on the ground, to investigate and control the outbreak and to intensify the planning for appropriate supplementary immunization activities.

Four cases of polio were confirmed on 20 April in just one governorate in the south-western part of the country, on the Red Sea coast. The latest 18 cases occurred across five governorates throughout Yemen, including in two districts in the country's capital Sanaa and suggesting the virus had spread across the country. Ongoing field investigations have identified additional suspected polio cases across the affected governorates in Yemen. Low immunization rates among Yemen's children may facilitate the spread of the virus.

Experts are now planning an outbreak response, using the recently-developed monovalent oral polio vaccine type 1(mOPV1). This new vaccine enables a precisely tailored immunological response to the type 1 poliovirus that is causing the outbreak. Compared to the commonly-used trivalent OPV, which offers protection against all three types of wild poliovirus, mOPV1 provides a greater immunity to type 1 wild poliovirus with fewer doses. Use of mOPV1 is expected during a nationwide immunization campaign in the second half of May. Yemen had already conducted a mass campaign on 11-14 April, as the country was considered to be at high-risk of polio re-infection from nearby Sudan where an outbreak of polio continues.

Experience in polio eradication demonstrates that outbreaks can be quickly contained with high quality immunization campaigns which reach every child under five years old.

Dedicated donor support and strong partnerships with the private sector have enabled the previous campaign in Yemen as well as swift development of the mOPV1 vaccine. However, a global funding gap of US$ 50 million must urgently be filled by July, to finance continued intensification of immunization campaigns in the second half of the year.

Global eradication efforts have reduced the number of polio cases from 350 000 annually in 1988 to 1267 cases in 2004. Six countries remain polio-endemic, with a further six where polio transmission is re-established. Concern is high that the ongoing outbreak of polio in Africa might lead to re-infection of more countries in the polio-free Horn of Africa and the Middle East. Yemen is the most recent of fifteen polio-free countries that have reported cases of polio since the epidemic began in late 2003.

Because of the development of the Salk and Sabin polio vaccines, polio was eliminated from the Americas in 1994, but it still circulates in Asia and Africa. The Global Polio Eradication Initiative, spearheaded by WHO, Rotary International, UNICEF and the CDC, was established in 1988 and seeks to make all countries polio-free. According to WHO, there currently are 1,263 polio cases worldwide and six countries where the virus is endemic. These are Nigeria, Niger, Egypt, Afghanistan, India and Pakistan.

The development of the Salk polio vaccine at the University of Pittsburgh is considered one of medicine's greatest milestones. April 12, 2005 marked the 50th anniversary of the announcement that the vaccine was declared "safe, effective and potent," and ushered in a new era in vaccine development. Since that time, 12 vaccines have been developed that protect against disease. But scientific, cultural and socioeconomic challenges must be addressed in order to develop effective and safe vaccines for such viruses as HIV, avian flu and malaria, and for those unknown viruses that could easily sicken or kill entire populations.

Background and Timeline of Current Epidemic

On 20 April, four polio cases due to wild poliovirus type 1 were confirmed in Yemen. The cases were reported from Hudeida governorate in south-west Yemen, on the Red Sea coast. Prior to these cases, wild poliovirus has not been found in Yemen since AFP surveillance commenced in 1996. On 4 April WHO Yemen was informed by Hudeida governorate health authorities of a cluster of acute flaccid paralysis (AFP) cases in children, the first cases of which had occurred in February 2005. The cases had been detected through AFP surveillance activities and investigated, including collection of stool specimens for laboratory investigation. On 18 April, in close coordination with local health authorities, two teams of WHO and Ministry of Health experts, including epidemiologists and paediatricians, were dispatched to Hudeida governorate to further investigate the cluster of AFP cases. On 20 April, results of testing of stool specimens of four of the cases by the polio network laboratory in Oman revealed wild poliovirus type 1. The laboratory and field investigation of other AFP cases is ongoing, and additional information will be made public as soon as it is available, including genetic information which will help identify the origin of the wild poliovirus responsible for the cases. Yemen already conducted a nationwide immunization campaign on 13-15 April, to immunize all of the country's 4.5 million children under the age of five years. WHO is working with the Ministry of Health in Yemen to plan for further intensive house-to-house immunization activities in the immediate geographic vicinity of the cases. Planning for the next nationwide immunization campaign to be conducted in the second half of May is being intensified. Contingency plans for a potential third campaign in June are being discussed. Additional technical support is being provided for the continuing investigation and for planning for immunization rounds.

WHO is working with the Ministry of Health in Yemen to ensure that AFP surveillance throughout the country is sensitized so that no transmission of wild poliovirus is missed. Additionally, Ministries of Health of neighbouring countries have been informed.

Important note

The risk of importations into polio-free areas remains as long as polio exists anywhere in the world. WHO urges all countries to maintain and strengthen AFP surveillance and high population immunity.

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