More than 100 million Covid-19 cases have now been recorded worldwide as newly-inaugurated US President Joe Biden pledged to ramp up America's struggling vaccine program. 

The number of cases, compiled from data provided by national health agencies, represents just a fraction of the real infections as the coronavirus has spread around the globe. 

The United States, which passed 25 million confirmed cases last weekend, remains the country with the largest outbreak -- and the largest death toll of over 420,000.