Washington: US President Joe Biden will lead a remembrance ceremony Monday to mark the dark milestone of 500,000 American Covid-19 deaths, but plans for easing the lockdown in Britain and a surge in vaccinations worldwide prompted growing optimism.With the US death toll on the brink of hitting half a million -- the highest impact on any country -- Biden ordered flags on federal government buildings to be flown at half mast for five days.The president was scheduled to address the nation from...