Medical personnel on Monday said they had started a trial of an experimental Ebola vaccine that may be used in neighbouring Democratic Republic of Congo, where an outbreak has killed more than 1,800 people.
The trial of the MVA-BN vaccine developed by Johnson&Johnson is expected to last two years, Uganda's Medical Research Council (MRC) said.
The vaccine will be administered to up to 800 health professionals and frontline workers such as cleaners, ambulance personnel and mortuary and burial teams, in the western district of Mbarara, the MRC said in a statement.
MRC spokeswoman Pamela Nabukenya Wairagala said vaccinations had already begun.
The MRC said the trial would be led by Ugandan researchers and supported by the London School of Hygiene and Tropical Medicine.
At present there is no licenced drug to prevent or treat Ebola although a range of experimental drugs are in development.
The Congo outbreak is the first time that a vaccine has been used as a full-scale weapon against the virus.
Health authorities have been issuing the rVSV-ZEBOV vaccine, developed by US pharma group Merck -- a product that has yet to be licenced but has been shown to be safe and effective.
The World Health Organization (WHO) has called for its deployment to be expanded and has recommended the Johnson&Johnson vaccine also be rolled out in order to meet needs.
However, the latter move has been resisted.
Critics have cautioned against introducing a new product in communities where mistrust of Ebola responders is already high.
Congo's former health minister, Oly Ilunga, who stepped down in July, was among the detractors.
The MRC said the Johnson&Johnson vaccine "is safe" and had been tested on more than 6,000 people in Europe, the US and African nations including Uganda.
However, its efficacy is unclear because it has never been assessed in an outbreak scenario.
By comparison, rVSV-ZEBOV was introduced in Guinea towards the end of a 2013-16 epidemic in West Africa, enabling scientists to conclude it was effective.
The trial taking place in Uganda, where there is no Ebola, will look at the response of the immune system to the vaccine -- a key pointer of effectiveness.
It will also look at safety and the attitudes of participants towards the vaccine, the MRC said.
Professor Pontiano Kaleebu, the lead Ugandan researcher in the trial, said developing a reliable vaccine was a key component to controlling Ebola epidemics.
"In this trial we hope to avail more information that will help us work towards having a licenced Ebola vaccine," Kaleebu said in a statement.
Uganda has suffered Ebola outbreaks in the past but nothing on the scale of the Congo epidemic, which began in August 2018.
It is the second-worst outbreak on record, eclipsed only by 2013-2016 epidemic in West Africa, which killed more than 11,300 out of 29,000 documented cases.
Uganda has been declared Ebola-free though in June three people from one family died there from the haemorrhagic fever after crossing back from Congo.