"Diplomatic platitudes are not enough—we need legal guarantees, and we need them now."Over 140 global leaders and experts on Thursday issued an open letter urging world powers to guarantee that both a coronavirus vaccine and any treatment for Covid-19, when available, be free for everyone in order to put the "the interests of all humanity" ahead of those of the wealthiest corporations and governments.The new letter, "Uniting Behind a People's Vaccine Against Covid-19," is signed by current and former heads of state. The global call comes days ahead of the World Health Organization's World Health Assembly. At that virtual meeting, scheduled for Monday, the letter signatories say health ministers must remember the WHO's founding principle to help achieve "the enjoyment of the highest attainable standard of health as a fundamental right of every human being."