A preprint published Monday shows that among 175 recovered COVID-19 patients from Shanghai, 30% showed a low neutralizing antibody response, with 10 patients showing undetectable antibodies. https://www.medrxiv.org/content/10.1101/2020.03.30.20047365v1

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Fortunately, apart from those 10 cases, serology can generally clearly distinguish between healthy and previously infected individuals.

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Antibody levels seem to spike at around 14 days of disease.

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There was a robust relationship between age and neutralizing antibody levels, with older patients having higher levels and with the large majority of cases of undetectable antibody levels in the younger patients.

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There was no decline in antibody levels when tested two weeks later.

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Duration of disease, length of stay, older age, and male gender were each correlated with higher antibody levels.

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Those with undetectable antibodies seemed to have a very mild course of disease.

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What this study seems to suggest is that serology clearly distinguishes between previously infected individuals and never-infected ones about 95% of the time but not always.

The implications of low antibody producers may yet to be fully understood. @venkmurthy @ethanjweiss

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