- Cohort of 18 patients with known transmission histories from previous 176
- Separate analysis of 18 patients at 6 months, 1, 2, and 3 years to obtain an IgG trend that more accurately represented convalescent SARS patients
- All 18 patients had positive IgG at 6 months and at 1 year 
- 1 patient became IgG negative at 2 years
- Only 55.56% of patients were IgG positive after 3 years 

Three year study of IgG Abs in selective cohort of convalescent SARS-CoV patients (related study)

- 176 cases from 7 designated SARS hospitals in Shanxi, China
- Day 7 after symptom onset, 11.8% of serum samples were IgG Abs positive
- From days 90-200, 100% of samples were IgG Abs positive
- After 1 year, 93.9% of samples were IgG Abs positive
- After 2 years, 89.6% of samples were IgG Abs positive
- 3 years later, only 50% of convalescent patients had SARS-CoV specific IgG Abs

Syracuse University

Several studies have shows a high correlation between specific IgG Abs and NAbs. Taken together, these studies revealed that the immune responses of specific Abs were maintained in over 90% of recovered SARS-CoV patients for 2 years.

Correlation between specific IgG Abs and NAbs

Lin, Q., Zhu, L., Ni, Z., Meng, H., &amp; You, L. (2020). Duration of serum neutralizing antibodies for SARS-CoV-2: Lessons from SARS-CoV infection. Journal of Microbiology, Immunology and Infection. doi:10.1016/j.jmii.2020.03.015
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7141458/ 

Duration of serum neutralizing antibodies for SARS-CoV-2: Lessons from SARS-CoV infection

- 56 cases from Beijing hospital of Armed Forces Police, China
- At four months, IgG Abs and NAbs peaked 
- After 16 months, titers gradually declined
- Before two years, IgG Abs and NAbs were detectable in all cases
- After 24 month mark, 11.8% of samples turned to negative 

Two-year cohort study measuring IgG Abs and NAbs levels in SARS-CoV patients

Fig. 1. The percentage of patients who expressed specific IgG Abs/NAbs against SARS-CoV in recovered patients

Three-year study of IgG Abs after SARS-CoV

After six years, specific IgG Abs to SARS-CoV were undetectable in 21/23 (91.3%) of recovered patients


FIGURE 1.
Dynamic changes in specific IgG Ab against SARS-CoV in patients who recovered from SARS. The geometric mean reciprocal titers (black line) are shown for the IgG Ab of the group of patients. The number of serum samples tested at each visit is given in the figure. The IgG titers of patient A (red line) and patient B (green line) are demonstrated.

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