A 'concerning' coronavirus cluster in Melbourne has now climbed to nine cases
Contact tracers are scrambling to track down the mystery link of infection
Latest cases are of the double mutant Indian strain, which is hyper-infectious
Three infected cases over-50 had not been vaccinated, despite being eligible
There are 43 venues on the outbreak's exposure list as of Wednesday morning
Alert issued after infected case attended the AFL game at the MCG on Sunday