Despite the billions of dollars spent on malaria programmes, the UN health agency said too many people are missing out on available resources like medicines and bed nets that protect against mosquitoes that spread the disease.
WHO had set a goal of cutting malaria cases to "near zero" by the end of last year. It fell far short, and now is aiming to reduce malaria cases and deaths by at least 90 per cent by 2030.
He said gains could be hurt by a lack of funding, which has stagnated in the last six years.
According to Tuesday's report, there were 212 million new cases of malaria and 429,000 deaths in 2015, a slight drop from the previous year. But the figures were based largely on patchy data and modeling; the report said surveillance systems catch fewer than 20 per cent of cases.
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The vast majority cases are in Africa. About 70 per cent of deaths are in children under 5.
Chris Drakeley, director of the malaria center at the London School of Hygiene and Tropical Medicine, said that even the incremental drop in malaria cases was significant. He noted that new approaches to fighting malaria like giving out medicines to children during high season to prevent infections were proving effective.
Other experts said WHO should rethink its priorities when it comes to malaria spending.
She said more money should be put into bed nets and health services instead.
"Even if you have a new vaccine, how will you even deliver it if there's no infrastructure?"
Harman questioned whether WHO's latest 2030 goal was realistic.
The WHO report said governments of malaria-endemic
countries provided about 31 per cent of total malaria funding in 2015.
The US is the largest international malaria fund provider, accounting for about 35 per cent of the total funding last year, followed by the UK (16 per cent).
The report also said between 2013 and 2015, 510 million insecticide treated mosquito nets (ITNs) were reported by manufacturers as having been delivered to countries in sub-Saharan Africa, which exceeds the minimum amount required to achieve universal access to an ITN in the household (491 million).
"Outside sub-Saharan Africa, 73 million ITNs were delivered by manufacturers between 2013 and 2015, with more than half of those deliveries accounted for by five countries (India, 13 million ITNs, Indonesia, 9.3 million, Myanmar 8.9 million, Cambodia, 4.3 million and Papua New Guinea 4.1 million)," the report said.
This figure includes 49 million people in WHO African Region and 44 million people in the WHO southeast Asia Region, of whom over 41 million are in India.
The report said in the WHO African Region, WHO Eastern Mediterranean Region, the WHO southeast Asia Region and the WHO Western Pacific Region, a large proportion of patients seek treatment in the private sector, and these cases are not captured by existing surveillance systems.
"The regional patterns are sometimes dominated by individual countries with the highest number of cases. For instance, a large proportion of patients in India seek treatment in the private sector," it said.