Sierra Leone - one of the countries worst hit by West Africa's Ebola outbreak - has announced a four-day lockdown to try to tackle the disease.

From 18 to 21 September people will not be allowed to leave their homes, a senior official said.

The aim of the move is to allow health workers to isolate new cases to prevent the disease from spreading further.

The outbreak has killed about 2,100 people in Sierra Leone, Liberia, Guinea and Nigeria in recent months.

The World Health Organization announced on Friday that health workers could be given vaccines as from November, when safety tests are completed.

More than 20 health workers have lost their lives to the virus in Sierra Leone since the start of the outbreak in March.

Last month Liberia sealed off a large slum in the capital Monrovia for more than a week in an attempt to try to contain the virus.

The disease infects humans through close contact with infected animals, including chimpanzees, fruit bats and forest antelope.

It then spreads between humans by direct contact with infected blood, bodily fluids or organs, or indirectly through contact with contaminated environments.
Ebola virus disease (EVD)

    Symptoms include high fever, bleeding and central nervous system damage
    Spread by body fluids, such as blood and saliva
    Fatality rate can reach 90% - but current outbreak has mortality rate of about 55%
    Incubation period is two to 21 days
    There is no proven vaccine or cure
    Supportive care such as rehydrating patients who have diarrhoea and vomiting can help recovery
    Fruit bats, a delicacy for some West Africans, are considered to be virus's natural host

BBC/TF