COVID-19 Antibodies
By Jessica Sarmiento PGY-3
The clinical implications of positive antibodies against Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has remained inconclusive. During times where herd immunity is most desired, it is important to analyze data on the serological studies of Antibody- positive patients, in order to elucidate on how vaccination against SARS-CoV-2 will be carried. In an article published on Nature Medicine June 18t,, 2020 titled “Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections”, the duration of antibody- mediated- immunity was analyzed.
In the Wanzou district of China, the close contacts of the symptomatic patients with confirmed RT-PCR SARS-CoV-2 infection were also quarantined, and once testing positive with RT-PCR, they were asked to provide demographic information and monitoring of symptoms for the upcoming 14 days. From 60 initial individuals who were transferred to a government-designated hospital for central isolation, a final number of 37 asymptomatic individuals were included in the study (prior being excluded for subsequent symptoms). These 37 asymptomatic individuals were matched to 37 symptomatic individuals as well as 37- matched control groups.
Data collected for all patients included CBC, CMP, LDH, CK, Coagulation profile, Ferritin, 48 cytokine/chemokines and Chest CT. Nasopharyngeal swabs tested by RT-PCR were obtained starting 1 week after admission and repeated every 2-3 days for the remainder of the hospital stay, defining SARS-CoV-2 negative as two consecutive RT-PCR results.
Upon analyzing the results, the median duration of viral shedding in the asymptomatic individual (from the first to last positive nasal swab) was 19 days, while those with mild symptoms was 14 days (statistically significant P=.028). Antibody titers were analyzed, including both IgM and IgG in the Acute phase (3-4 weeks after exposure) and IgG in the Early convalescent phase (8 weeks post-discharge from the hospital). In the Acute phase, IgG levels were higher in the Symptomatic group when compared to the Asymptomatic group (P=.005), and the IgM levels were also higher in the Symptomatic group when compared to the Asymptomatic group, but was not found to be statistically significant. In the Early Convalescent phase, the IgG levels declined in both groups when compared to the levels in the Acute phase. The most striking result was that 40% of the Asymptomatic group became seronegative for IgG, in comparison to only 12.9% of the Symptomatic group.
Limitations to this study include generalizability as this included a select population in China (not diversified amongst different countries), as well as environmental differences, as these 37 asymptomatic individuals were monitored within a hospital versus most asymptomatic individuals in the United states being quarantined in their homes). Patients were also specifically selected after known close contact exposure to RT-PCR positive/symptomatic patient, meaning there was no randomization. Although the study had a small population size, it was surprising to see how quickly the antibody titers can decrease, to the extent of becoming seronegative in a proportion of the individuals. Further larger scale studies must be done to analyze antibody mediated immunity duration, prior to releasing vaccines against SARS-CoV-2 to the general public.
Long, Q., Tang, X., Shi, Q. et al. Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections. Nat Med 26, 1200–1204 (2020). https://doi.org/10.1038/s41591-020-0965-6