Rapid Drop of Antibodies in Mild COVID-19 patients

A fast drop in COVID-19 antibodies in mild patients triggers the alarm for protection against the new virus.

This decrease, observed within the first 90 days after contagion, might slow down over time. However, it calls for caution when it comes to the feeling of “protection” in recovered patients, vaccine immunization at long-term, and ultimately the prospect of an “immunity passport”. 

A recent article published in Nat Med had suggested a rapid fall in IgG anti SARS-CoV-2 antibodies, though with no details. Instead, this new study (now published in NEJM) sheds new light and supports all suspicions. 

COVID-19 was confirmed via PCR in the entire cohort except for 4 patients that showed no symptoms despite having lived with a confirmed infected patient. These 4 were not tested because they had a mild infection and testing resources were scarce.

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Most patients enrolled had mild symptoms and were young (mean age 43). Only two required low-flow supplemental oxygen. They all had serial measurements of IgG levels, two, and even three times. 

The first measurement was obtained at mean 37 days after symptom onset and the second at mean 86 days. 

The initial mean IgG level was 3.48 log10 ng per milliliter based on a linear regression model that included age and sex, and the number of days from symptom onset to the first measurement and first antibody level.

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This allowed estimating a half-life of approximately 36 days for the observation period. 

The protective role of SARS-CoV-2 antibodies is still unknown, but in general they correlate relatively well with virus immunity. Plasma level of IgG corresponds to our bodies’ capacity to block virus entry. 

The nearly exponential loss of antibodies after acute exposure to viral antigens casts a shadow on humoral immunity in line with an article published by Long et al.  in Nat Med.

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It is difficult to extrapolate observations of this study beyond 90 days, even though the fall will likely stabilize after this period. 

More studies are necessary to know the quantitative protection of these antibodies in the mid and long terms. 

Título original: Rapid Decay of Anti–SARS-CoV-2 Antibodies in Persons with Mild Covid-19.

Referencia: F. Javier Ibarrondo et al. NEJM 2020, online before print. DOI:10.1056/NEJMc2025179.

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