New Delhi, April 24 -- Covid-19 will continue to be a problem and "variants will keep getting scarier and scarier" until at least two-thirds of the global population is vaccinated, one of the world's foremost scientists has said, calling for efforts to minimise the inequity that has left large parts of the world without access to doses. The comments were made by Dr Drew Weissman, professor of medicine at University of Pennsylvania's Perelman medical school, who, along with his long-time collaborator Dr Katalin Kariko, is credited with the research that underpins the success of mRNA vaccines by Pfizer-BioNTech and Moderna....