How long does COVID immunity last?


The time course of antibody production following SARS-CoV-2 infection was analysed using blood samples obtained from antibody screening of patients with known/suspected COVID-19 at Mount Sinai, New York (Wajnberg et al. Science 2020;370:1227-1230). The assay was the Mount Sinai ELISA that characterizes the antibody response to the Spike protein and has high sensitivity and specificity (92.5%, 100%).

A total of 30,082 subjects tested positive, defined as detectable antibodies to Spike protein at a titre of 1:80 or higher. Titres were classified as low (1:80 and 1:160), moderate (1:320) and high (1:1960 and >1:2880). The proportion of positive samples was 7.12% low, 22.49% moderate, and 70.39% high. Prior testing also showed that >95% of PCR-confirmed COVID-19 cases have positive antibody titres. Neutralizing activity was determined in 50% of low-titre samples, 90% of moderate-titre samples and 100% of high-titre samples.

A subset of patients was followed up at 82 days (range 52-104 days) and 148 days (range 113-186 days) after symptom onset. There was a slight drop in geometric mean titre (GMT) at the first (764 to 690) and second (690 to 404) follow-ups. Subjects with initially low titres saw increasing titres to day 82 before declining at day 148. Levels were undetectable during follow-up in a few individuals with very low initial titres.

The results suggest that most patients with COVID-19 mount a robust antibody response, and that neutralizing antibody production is sustained for at least 5 months. It is unclear if the durable response will provide protection against reinfection, notably by CoV-2 variants, but may reduce the severity of reinfection.

Preliminary results have shown that a robust antibody response to the Moderna mRNA vaccine is maintained for at least three months (Widge et al. N Engl J Med 2021;384:80-82). GMTs were similar across age groups, including in those aged >70 years.

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