Some 156 nations have joined a global scheme for fair distribution of future vaccines against Covid-19, an alliance led by the World Health Organization (WHO) said on Monday, but superpowers China and the United States did not sign up.US President Donald Trump’s government has already secured future supplies through bilateral deals, prompting accusations of selfish behaviour to the detriment of poor countries.China, where the coronavirus was first reported, was also missing on the list of 64…