EMMA FARGE  THE head of UNICEF has asked G7 countries to donate supplies to the COVAX vaccine-sharing scheme as an emergency measure to address a severe shortfall caused by disruption to Indian vaccine exports. India has curbed exports of the AstraZeneca vaccine made by its Serum Institute, which had been pledged to COVAX, to be used by the country as it battles a massive second wave of infections. U.N. agency UNICEF, which is in charge of supplying coronavirus vaccines through COVAX, estimates the supply shortfall at 140 million doses by the end of May and about 190 million by the…