In the rush to re-open the world’s economies, an idea has been taking shape: field a workforce of survivors who can be shown to have Covid-19 antibodies. But history urges caution.

One hurdle is scientific. The gold standard, testing that detects HIV antibodies, took years to develop, so it should come as no surprise that creating a specific and sensitive test for the new coronavirus has proved tricky. Moreover, it remains unclear whether the presence of antibodies confers lasting immunity to Covid-19.

A second obstacle is social: What would creating a privileged workforce do to a society that is already stratified? While companies are rushing out digital certification apps they promise can act as passports for a new workforce, science historians and ethicists are raising an alarm. They say a great deal can be learned from looking back in history to times when desperate people would “buy the pox,” and survival after yellow fever became more than the ultimate resume enhancement.