The World Health Organization is looking at new financial instruments to help to fill a $28 billion funding shortfall for tools to fight COVID-19, a senior official said on Tuesday.

The WHO and GAVI vaccine alliance aim to provide poor and middle-income countries with diagnostic tests, drugs and vaccines through a fund known as the Access to COVID-19 Tools (ACT) Accelerator, which was set up last April.

Bruce Aylward, a senior WHO adviser and its ACT coordinator, said that new financing mechanisms - including concessional loans and catastrophe bonds - were discussed at a meeting of the ACT facilitation council on Monday, co-chaired by Norway and South Africa.

"Right now financing is what stands between us and getting out of this pandemic as rapidly as possible," he told a U.N. briefing in Geneva.

"It's a real challenge in today's fiscal environment despite the fact that this is the best deal in town," Aylward said, referring to the ACT Accelerator facility. "This will pay itself off in 36 hours once we get trade and travel moving again."

Aylward said that the WHO and partners were in talks with Pfizer to include its COVID-19 vaccine as part of an early global rollout.

He said that he saw a "strong commitment" on the part of Pfizer CEO Albert Bourla to set prices at levels appropriate to poorer populations. Aylward expected some news on more manufacturers joining the list of providers to the COVAX vaccine facility in coming weeks, he said.

Canada has pledged to spend C$485 million ($380 million) to support COVID-19 tests, treatments and vaccines in low- and middle-income countries, including antibody treatments, International Aid Minister Karina Gould said on Monday.