Hong Kong scientists teaching a panicked populace to make their own surgical masks with paper towels and metallic wire must surely rank as one of the most Kafkaesque moments of the new coronavirus disease outbreak. But the worst is yet to be if global medical supply chains, already stretched in parts to breaking point, are not shored up to cope with the pandemic.

A desperate shortage of surgical masks, the most visible symbol of the epidemic since China began fighting it at the start of the year, underscores the scale of the problem. The country made five billion masks last year and supplied about half of the global market. But with its people churning through tens of millions of masks every day, China is cranking up domestic production even as it imports medical gear from the West.

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