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COVID-19: Waning Antibodies / Seroprevalence of Antibodies / Thromboses

By Kelly Young at NEJM Journal Watch

Today brings a flurry of research on SARS-CoV-2 antibodies:

Waning antibody levels after mild illness: Thirty-four volunteers who had recovered from COVID-19 illness — mostly mild — had their IgG antibody levels assessed at a mean of 37 and 86 days after symptom onset. The observed reduction in IgG levels corresponded to a half-life of roughly 73 days. The authors write in the New England Journal of Medicine: "Our findings raise concern that humoral immunity against SARS-CoV-2 may not be long lasting in persons with mild illness, who compose the majority of persons with Covid-19. It is difficult to extrapolate beyond our observation period of approximately 90 days because it is likely that the decay will decelerate."

U.S. antibody seroprevalence: A new CDC study in JAMA Internal Medicine paints a picture of undetected SARS-CoV-2 infections around the U.S. through mid-May. Researchers tested 16,000 serum samples collected for routine screening or clinical management from 10 sites around the U.S. from March 23 to May 12. The seroprevalence of SARS-CoV-2 antibodies ranged from 1% in San Francisco to 7% in New York City. Based on seroprevalence, the authors estimated that in Missouri, 24 times more people may have been infected than what had been reported, and at six other sites, estimates were 10 times higher than what was reported. Despite these seemingly large estimates, editorialists write in JAMA, "the study rebukes the idea that current population-wide levels of acquired immunity (so-called herd immunity) will pose any substantial impediment to the continued propagation of SARS-CoV-2 in the US, at least for now." Separately, in MMWR, 3% of the population of Indiana aged 12 and up had either current or previous SARS-CoV-2 infection in late April, and in the Atlanta area in late April to early May, the seroprevalence of antibodies was around 3%.

Thromboses: Roughly 16% of patients hospitalized with COVID-19 at a New York hospital had a thrombotic event, according to a JAMA research letter. All-cause mortality was higher among those who experienced a thrombotic event (43% vs. 21%). Higher D-dimer levels at presentation were predictive of thromboses.

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