The Ebola epidemic seems to have reached a turning point, as cases fall in all three of the worst-hit countries of west Africa, according to World Health Organisation figures.

Last week there were fewer than 150 cases reported, with Sierra Leone accounting for most of them – 117 of the total. The previous week it reported 184 cases and the week before 248. At the peak in December, the country was reporting 550 cases a week. Liberia’s case numbers have dropped from a high point of more than 300 a week in August and September. This week it reported eight, while the total for Guinea was 20.

Dr Christopher Dye, the director of strategy in the office of the WHO director general, told the BBC News website: “The incidence is pretty clearly going down in all three countries now.

“Each of the last three weeks has been the most promising we’ve seen so far, the message is reductions in all places.”

Dr David Nabarro, the UN secretary general’s special envoy on Ebola, and senior coordinator of the response, said the outbreak was diminishing, while insisting: “I want all to be vigilant.”

Nabarro, who is now at the World Economic Forum in Davos to discuss funding for fighting the epidemic, told the Guardian the UN was now looking for $1bn more to add to the $1bn that governments, international organisations and philanthropists have already donated. That is $500,000 more than has so far been pledged.

“It will be hard to raise, but the last bit – getting to zero – is the most difficult and is very expensive,” he said.

In an interview in London earlier this week, he said the money would be needed to ensure a fast and flexible response to any new outbreaks, using helicopters to access remoter regions and bring in the personnel needed, as well as carrying out the intensive detective work of tracing contacts to ensure everybody who is infected is treated and isolated.

But the rhetoric around the epidemic has changed. Last October, the WHO was warning that the number of new infections was doubling every four weeks. The Centers for Disease Control in the US estimated that there could be 1.4m cases by this month.

Now, WHO is talking of new case numbers halving. In Guinea, where they are dropping fastest, the numbers are halving every 10 days, in Liberia every 14 days and in Sierra Leone every 19 days. There have been 21,724 reported cases so far and 8,641 officially recorded Ebola deaths. The true figures are believed to be much higher.

Experts are warning, however, that Ebola outbreaks can flare up again just as quickly as they die down. In Guinea, the pattern has been a sequence of rises and falls. Mali has been declared free of the virus, but, said the WHO: “Surveillance and information sharing will be increased in the border districts of Guinea-Bissau, Côte d’Ivoire, Mali and Senegal adjacent to the three intense-transmission countries.”

In the worst affected countries, there are long-awaited moves to return life to something closer to normality. Schools in Guinea have begun to reopen after five months’ closure. The decision was sudden, with staff and parents given just four days’ notice. Both Liberia and Sierra Leone have also said schools will reopen.

The closures were ordered to avoid mass gatherings where people would come into physical contact and there was a risk that transmission of the virus would occur. Public meetings, political rallies and even football games were also halted and curfews were imposed on roads at night to prevent people travelling.

In Liberia, where the first signs of a drop in cases were seen, the government is treating the apparent slowing of the disease with “very cautious optimism”, said information minister Lewis Brown.

However, he stressed there was no room for complacency and warned that the slightest lapse in vigilance could yet prove disastrous. “We are determined that as the cases continue to go down, there is no recurrence,” he told the Guardian. “We may have got a handle on the transmission of the virus; we may be in a position to isolate and treat people quickly. But this is a virus which, given our sociology and health infrastructure, could spread again very, very quickly. So we have to make sure that no one has any false sense that the hard work’s done.

“When you add the fact that we share very porous borders with both Sierra Leone and Guinea, you can understand why, even as our numbers go down, we remain very cautiously optimistic.”

He added: “We continue to call for a regional approach to ending this scourge; none of us can be safe until all of us are safe.”

The epidemic has continued to take a severe toll of health workers, who are exposed to the greatest risk by their physical contact with those who are sick. In total, 828 have been infected across the three countries and 499 have reportedly died, says the WHO. The numbers becoming infected in Liberia and Sierra Leone have fallen but they rose in Guinea in December.

Baroness Amos

Guinea’s president, Alpha Condé, yesterday called on the International Monetary Fund to provide debt relief to help his Ebola-stricken country build a health system capable of preventing a future epidemic.

Condé was meeting Christine Lagarde, the IMF’s managing director and the World Bank president Jim Kim at the Davos World Economic Forum in an attempt to reduce payments to Guinea’s creditors.

The country has been one of the three West African countries affected by the Ebola virus, and Condé said any help provided would be re-cycled into health.

His call came as Baroness Amos, UN undersecretary for humanitarian affairs and emergency relief, hit out against the way the international community responded to the Ebola crisis. Amos said that much more support was needed, with better co-ordination and a more long-term approach.

“We should not be having to scramble around to raise money to put in place to set up the supply chains,” said Amos, who was speaking on a separate panel to Condé.

She said the three countries currently being dealt with – Guinea, Sierra Leone and Liberia – were post conflict. “I think we are way too short-term, we have to be in for the longer term. We have to say as a global community to say we are going to be with you for the next, 20 years, for example.”

But she highlighted the difficulties in coordinating the various bodies and said governments businesses and NGOs needed to work together. “We have agencies with separate and overlapping mandates, we are highly bureaucratic,” she said.

Jill Treanor and Larry Elliott at Davos