STEPHANIE NEBEHAY and EMMA FARGE 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, 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…