Researchers who studied antibody responses in 30,000 patients with mild-to-moderate COVID-19 report that the patients' antibodies were relatively stable for at least five months. Although the results do not yet provide conclusive evidence that these levels protect from reinfection, Ania Wajnberg and colleagues say they "believe it is very likely that they will decrease the odds ratio of reinfection and may attenuate disease in the case of breakthrough infection." As the number of daily COVID-19 cases worldwide continues to mount, the nature of the humoral immune response, which includes an antibody response, remains uncertain. Assessing the antibody response in mild and asymptomatic cases is of particular importance since these cases constitute the majority of infections. In March 2020, the Mount Sinai Health System in New York City began to screen individuals for antibodies to SARS-CoV-2 to recruit volunteers as donors for convalescent plasma therapy. By 6 October, Mount Sinai had screened 72,401 individuals, with a total of 30,082 individuals testing positive, many of whom showed notable IgG antibody responses. Wajnberg and colleagues studied this cohort to dissect the longevity and potency of their anti-SARS-CoV-2 antibody responses. Using a well-established assay, they evaluated neutralizing effects of the antibodies, critical to understanding possible protective effects. They report that spike binding as measured by the assay is roughly correlated with virus neutralization. To evaluate longevity of the antibody response, the authors recalled 121 plasma donors. In these patients, they found stable antibody titers for a period approximating five months. The authors note their findings contradict other work suggesting antibody responses do not have much longevity, including work published in June 2020 that showed waning titers eight weeks after virus infection. However, among other differences, the antibodies measured in that report targeted a different viral antigen. This may suggest the stability of the antibody response over time depends on the target antigen, the authors say. They plan to follow their cohort over longer intervals to help inform if and how enduring antibody responses protect from reinfection. "We believe it is imperative to swiftly perform studies to investigate and establish a correlate of protection from infection with SARS-CoV-2." This could inform policy regarding the COVID-19 pandemic, they say, and would be beneficial to vaccine development efforts.