LONDON • An experimental Ebola vaccine from Johnson & Johnson (J&J) sits idle in a Dutch warehouse, ready to help counter the international crisis erupting in Africa - if the authorities decide to use it.

The Ebola epidemic that began a year ago has already killed over 1,700 people and was declared a global public health emergency last Wednesday. World Health Organisation (WHO) officials say they have about 245,000 doses of an experimental vaccine from Merck that is already in use, and there is a need for additional options.

Health leaders in the Democratic Republic of Congo are reluctant to roll out J&J's vaccine alongside Merck's because their differing regimens may lead to confusion in the conflict-riven region of the outbreak. Both products are experimental and are yet to be licensed.

Still, as the virus continues to spread, health experts and the humanitarian group Medecins Sans Frontieres say it is imperative that vaccination coverage in the region be extended.

"We must use all of the tools and approaches at our disposal, including the coordinated use of both the Merck and J&J vaccines," Dr Peter Piot, director of the London School of Hygiene and Tropical Medicine, said in a statement. He was among the team who discovered Ebola.

The Merck vaccine has already been given to at least 143,000 people in the latest outbreak, according to a report from Congo's Ministry of Health. The remaining supply could be doubled to about 500,000 by splitting doses in half, an approach that was shown to be effective when used in Guinea, the report said.

J&J's shot is one of four other experimental vaccines that officials have discussed using. The company has been working on the product, which also includes a shot developed by Bavarian Nordic, for over a decade, according to Mr Paul Stoffels, chief scientific officer of the US healthcare giant.

While it still has not gained approval from health officials, studies in humans and animals suggest it is safe, effective and provides long-lasting immunity against Ebola.

But there are important differences from Merck's vaccine that have to be taken into account, Mr Stoffels said. Made from a live, replicating virus, Merck's vaccine mounts protection against Ebola in about 10 days. While the J&J immunisation appears to raise the body's defences for the long term, it is administered in two shots about two months apart.

How much, if any, protection a person gets from the first shot before getting the second is not clear. Ensuring people are fully vaccinated with the two-shot regimen would be challenging among mobile populations, especially in people fleeing conflict.

Late-June meetings with WHO and other health groups concluded that J&J's vaccine should be tested in the country, but in areas outside the epidemic "hot zone" to reduce the chance that erroneous perceptions about the differing shots will lead people to refuse vaccination, the report said. Usage would also have to be closely monitored as part of a clinical study. The J&J vaccine is tested regularly for stability, is in good condition, and will probably remain usable for another five or 10 years, Mr Stoffels said.

"If the epidemic gets under control quickly and there's no need for it, we'll happily store it for the next one," he said. "As a company, we stand by with 1.5 million doses of vaccine when people want to deploy them."

BLOOMBERG