Global coronavirus cases neared 30 million on Thursday, as a study showed rich nations representing a fraction of the world’s population have already bought over half the promised Covid-19 vaccine stocks.Pharmaceutical companies are racing to produce an effective jab to counter a virus that has now killed more than 940,000 people around the world, according to a Johns Hopkins University tally.European Union chief Ursula von der Leyen on Wednesday warned against “vaccine nationalism” that she…