Spain has had one of the worst Covid-19 outbreaks in the world, which makes a recently completed antibody-testing study of the Spanish population so significant — and so scary.

Preliminary results from a well-designed survey of antibody presence among Spaniards suggest that even as the Spanish outbreak exploded and then was brought under control, only 5 percent of the country’s population has been infected with the coronavirus so far. This means that the vast majority of the Spanish population remains susceptible to infection if the lifting of restrictions there leads to a new spike in cases.