OF THE VARIOUS ideas being touted to ease the world out of viral lockdown, one of the most striking is that of giving "immunity passports" to those who test positive for antibodies to SARS-COV-2, the virus that causes covid-19. These passes would let people move around and return to work-based on the assumption that possession of such antibodies prevents reinfection. This might sound like a reasonable assumption. It is, after all, true of many other infections. Assumptions, however, are not data. So on April 24th the World Health Organisation issued a briefing note on why immunity passports are not a good idea: "There is currently no evidence", it said, "that people who have recovered from covid-19 and have antibodies are protected from a second infection." Medical researchers have learned a lot about SARS-COV-2 in the months since it was first isolated. But their knowledge of its interactions with the human immune system remains gappy. What are the specifics of the immune system's response? How does this response affect the severity of someone's illness? How long does immunity last? Lack of such knowledge makes it hard to decide when to relax restrictions on movement and association. Do it too soon and you risk a viral resurgence. Do it too late and you risk having no economy for people to return to.
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