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Sometime in the late 1980s, in a town in southwest England called Salisbury, 15 volunteers agreed to have a cold-causing coronavirus known as 229E squirted into their noses in a saline solution. Ten of the volunteers were successfully infected, as determined by viruses recovered from their noses in the days following, although only eight displayed symptoms. Researchers monitored the levels of antibodies and immune cells in their blood over the ensuing weeks.
A year later, 14 of the same volunteers came back for another round. Of the nine people who’d become infected with the first exposure, six became infected again, but none developed colds. Moreover, they only shed virus from their noses for a couple of days, compared with an average of five and a half days the first time around. As for the five people who’d resisted infection the first time around, all became infected ...
