Yemen is about to embark on its seventh round of national immunisation days against polio this year, in an unprecedented effort to stamp out the disease following a serious outbreak which began last February.
During three consecutive days, tens of thousands of vaccination teams will visit every household in order to deliver the oral polio vaccine to all of Yemen's estimated 4 million children aged under five.
National immunisation days require huge investments of time, money, health workers and other resources. It is unusual for a country to carry out more than three rounds in one year. Yemen's seven rounds follow an outbreak of polio earlier this year in which a total of 476 cases were reported. This incidence is second only to Nigeria where 590 cases have been recorded in 2005. Yemen's outbreak began in February and reached its apex in May. Previously, Yemen had been free of polio since 2000.
The Polio Eradication Initiative was launched by the World Health Organization, Rotary International, the US Centers for Disease Control and Prevention, UNICEF, and national governments in 1988 to eliminate the paralysing disease from the world. The end of 2005 had become defined as a deadline for this achievement.
However, eradication efforts suffered a setback in August 2003 when children in several Northern Nigerian states were prevented from receiving the oral polio vaccine. Governors of these states banned immunisation activities; citing concerns that the vaccines might contain HIV and sterilising agents (BMJ 2003;327:380, 9 August).
Following the cessation of immunisation activities, the number of polio cases rose sharply in the region. During 2004 and 2005 the poliovirus spread from Nigeria to other African countries and eventually across the Red Sea to Yemen.
Yemen is one of several countries that has experienced epidemics of imported cases of polio this year. Polio now remains endemic in just six countries worldwide: Nigeria, India, Pakistan, Niger, Afghanistan, and Egypt.
Eradication efforts reduced the global incidence of polio from 350 000 cases in 1988 to an all time low of less than 700 cases in 2003. However, following Nigeria's outbreak and subsequent spread of the disease, the number of global cases rose to 1255 in 2004 and to 1567 so far in 2005. The deadline for worldwide eradication of polio has now been pushed back from the end of 2005 to 2008.