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.

Accountable US, a nonpartisan taxpayers’ advocacy group, has calculated that from the start of the federally coordinated effort to develop vaccines on May 15 until August 31, officials at five pharmaceutical companies made more than $145 million by selling shares.