A debate is raging over proposals that a second vaccine be introduced to fight Ebola in Democratic Republic of Congo, currently in the grip of its worst outbreak.
The DR Congo Health Minister, Dr Oly Ilunga, who resigned after being stripped of management of the country's Ebola response, said the current vaccine is the only one that has been proven to be effective, and an opposition MP said the new vaccine is untested, and fears people in the country will be used as guinea pigs.
Leading health experts say the second vaccine is safe and could be an important tool in holding back the spread of the virus.
So what are the concerns, and are they justified?
Tried and tested?
It has been tested on 6,000 people and "has shown outstanding safety," says Professor Peter Piot, a leading expert on Ebola and director of the London School of Hygiene & Tropical Medicine, which has been involved with pharmaceutical company Johnson & Johnson in the development of the vaccine.
Studies have shown that although the drug is still in the experimental phase and hasn't been tested on patients with Ebola, it has proved highly effective in tests on primates (animals genetically close to humans).
The only way to test it on humans is for it to be used in an outbreak scenario, as it wouldn't be safe to trial the medicine on volunteers infected with the virus in a clinical trial.
This is how the first vaccine – by the Merck & Co drug company – was successfully deployed in Guinea in 2015.
It was rolled out for "compassionate use" which allows for the use of an unlicensed drug (licenses can take years or decades to get) when no other options are available, but only with authorisation from the government of the affected country.
- Ebola: One year on from Democratic Republic Congo outbreak
- The impact of militant attacks in DR Congo
- Rwanda shuts border with DR Congo to stop spread of virus
World Health Organization (WHO) data shows the Merck vaccine has a 97.5% efficacy rate for those who are immunised, compared to those who are not.
The WHO says this vaccine is proven safe and effective against Ebola, but that more testing is still needed for it to be licensed.
So, we're in a similar place with the new vaccine as we were in 2015 with the current one – there's substantial evidence that it's safe and that it could be effective, but it hasn't been tested in an outbreak, and hasn't been licensed./BBC news