The World Health Organization published a target product profile for covid-19 vaccines that specified minimum characteristics to guide developers—including 50% efficacy.1 These are only aspirational, however, and neither companies nor regulators are bound to follow them. Officials from both the US Food and Drug Administration (FDA) and the European Medicines Agency have already signalled that they would consider approving vaccines that only diminished severity of illness, rather than protected against infection.

Meanwhile, companies have suggested acceptable efficacy goals much lower than 50% and have forewarned that protection may be relatively short lived. Key vaccine characteristics that are known to be critical for successful rollout globally—such as immunisation schedule (ideally a single dose), temperature stability (ideally no refrigeration), potential for rapid scale-up of manufacturing, and low cost—are currently not being considered in the competition for marketing approval. WHO has proposed a trial protocol that aims to test and compare different vaccine candidates in a standardised way, which would allow the best to be prioritised.

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