SARS-CoV-2 is a betacoronavirus responsible for COVID-19. The viral envelope Spike (S) proteins bind to host cell angiotensin-converting enzyme 2 (ACE-2) receptors via the receptor-binding domain (RBD) to facilitate viral entry. Following infection, IgM, IgA, and IgG antibodies are typically produced within 1 to 2 weeks post-onset of symptoms (POS), with neutralizing antibodies (nAbs) remaining detectable for 12 to 34 months.

Princeton University

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This study examined serological testing, antibodies against reinfection, and durability of vaccine protection in order to answer the question of whether or not neutralizing antibodies provide protection against reinfection of SARS-CoV-2 and to determine the length of antibody responses. 

- Important Definitions and Background Information
- Methods
- Patients
- Results
- Discussion

Longitudinal Evaluation and Decline of Antibody Responses in SARS-CoV-2 Infection

- The optical density at 1:50 serum dilution was measured for 300 samples from the 65 patients. 2/65 individuals did not have a measurable antibody response, most likely due to the fact that their sera were only available up to 2- and 8-days POS. It is probable that they seroconverted at a later time point after they were discharged from the hospital (with the average seroconversion against at least 1 antigen being 12.6 days POS).
- IgG responses against S, RBD, and N antigens were observed in 92.3%, 89.2% and 93.8% of individuals respectively. IgM responses against S, RBD, and N antigens were observed in 92.3%, 92.3% and 95.4% of individuals. The percentage of individuals with IgA responses to RBD and N was lower, with only 72.3% and 84.6% seropositive respectively, but the percentage for that of IgA against S was around the same as IgG and IgM. 
- 51.6% of individuals showed synchronous seroconversion to IgG, IgM and IgA while 9.7%, 9.7%, and 9.7% of individuals showed singular seroconversion to IgG, IgM, and IgA, respectively. 
- 58.1% of individuals showed synchronous seroconversion to S, RBD and N, whereas 16.1% of individuals showed singular seroconversion to either N or S. 
- Both IgM and IgA responses to all three antigens declined between 20 and 30 days POS respectively. On the other hand, the IgG response remained high even up to 94 days POS. Differences were observed with disease severity and when half maximal binding (EC50) was measured. 


Antibody Binding Responses to SARS-CoV-2


Neutralizing Antibody Responses to SARS-CoV-2


Longevity of the Ab Response


- Serum samples from 31 seropositive healthcare workers were analyzed. 80.6% had COVID-19 compatible symptoms while the remaining had none.
- ID50 values correlated with the optical density values for IgG and IgM against S and RBD, but correlated poorly for those against N.
- Asymptomatic individuals and symptomatic healthcare workers had similar and lower ID50 values compared to those who were hospitalized in the 0-3 and 4/5 severity groups.
- Due to the lower mean ID50 values within healthcare workers, the decline in nAb titres were more frequent than that of patients 


Ab Responses in a Healthcare Worker Cohort


65 RT-qPCR confirmed SARS-CoV-2 infected individuals

- 59 admitted and 6 healthcare workers at Guys' and St. Thomas' NHS Foundation Trust 
- 77.2% male
-Average age: 55.2 years (ranging from 23-95 years)
- Information on ethnicity was not collected

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