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Higher convalescent plasma antibody titre levels associated with lower risk of death in COVID-19

Passive antibody transfer (convalescent plasma therapy) has been widely used to treat COVID-19; however, little is known about the effect on mortality of different antibody titre levels.

The use of convalescent plasma (CP) to treat respiratory infections has a long history having been used for over a century. During the current pandemic, interest in this therapeutic modality has picked up although the efficacy signals from this approach are still preliminary and require further study. As a result, a team led by researchers from the Department of Anaesthesiology and Peri-operative Medicine, Rochester, Minnesota, in the US, retrospectively studied the results obtained from an expanded-access programme to CP across a range of hospitals. Eligible patients were 18 years and over, hospitalised with a laboratory confirmed positive COVID-19 test and deemed at high risk for progression to severe or life-threatening COVID-19.

Treatment consisted of CP given intravenously although the corresponding IgG COVID-19 antibody levels within these samples were unknown. The researchers therefore collected and quantitively analysed, remnant aliquots of serum retained from the donation process for IgG antibody levels. These which were divided into low (<4.62), medium (4.62 to 18.45) and high (>18.45) titre levels. The primary outcome for the study was mortality at 30 days after transfusion of CP.

The patient cohort consisted of 3082 individuals of whom, 61% were male and 69% were younger than 70 years of age. In total, two-thirds received CP prior to mechanical ventilation. Death within 30 days after CP occurred in a 26.9% of all patients. Furthermore, the outcome occurred in 29.6%, 27.4% and 22.3% of those in the low, medium and high, IgG titre ranges respectively. The risk of death among those with higher antibody titre levels was reduced by 46% compared to the lowest antibody titre (relative risk, RR = 0.66, 95% CI 0.48-0.91) in patients who were not mechanically ventilated. However, there was no effect of antibody titre levels on death rates among patients who required mechanical ventilation.

The authors concluded that their data support the notion that the benefits of CP are largely dependent on the levels of antibody present within samples.

Joyner MJ et al. Convalescent plasma antibody levels and the risk of death from COVID-19. N Engl J Med 2021