Pfizer, Moderna, Novavax: executives at several American laboratories developing Covid-19 vaccines have recently pocketed millions of dollars by selling shares in their companies -- raising questions about the propriety of such a move in the midst of a national health crisis.On the very day that pharmaceutical giant Pfizer announced preliminary data showing its vaccine was 90% effective against the coronavirus, its chief executive Albert Bourla sold shares worth $5.6 million.There was nothing illegal about this, Pfizer said: the sale took place according to rules allowing company heads to sell shares under predetermined criteria, at a date or for a price set in advance, to avoid any suspicion of insider training.Under the same rules,.