- In baseline testing at 2-3 weeks, 48% of Covid-19 patients had a positive IgG response, and at 8-12 weeks, 77.8% had a positive response. 
- The majority (72%) of patients showed an increase in IgG levels between the baseline and follow up testing. Those who had contact with infected individuals but never developed Covid showed no positive IgG levels at follow up testing. 
- For IgA response, 76% of Covid patients showed elevated levels at baseline, but only 32% showed elevated levels at the follow up. And, some patients with no IgA levels at baseline still later developed IgG levels at the follow up. 

Georgetown University

This study followed the immune response of Covid-19 patients and contacts in a controlled outbreak over 12 weeks to determine whether the immune response of Covid-19 patients increased over time, and whether exposure without infection causes a silent immune response.

- Methods 
- Results
- Discussion

Immune response to SARS-CoV-2 in health care workers following a COVID-19 outbreak: A prospective longitudinal study

Malferheiner, Sara et al. (2020) Immune response to SARS-CoV-2 in health care workers following a COVID-19 outbreak: A prospective longitudinal study doi: 10.1016/j.jcv.2020.104575

Immune response to SARS-CoV-2 in health care workers following a COVID-19 outbreak: A prospective longitudinal study


The serological response of health-care workers during a covid-19 outbreak was documented over a 12 week period. Serological testing was first performed 2-4 weeks after the outbreak and then again 8-12 weeks after to document the change in immune response over time. Testing was done by the Anti-SARS-CoV-2 IgG and IgA ELISA, and the Elecsys Anti-SARS-CoV-2 to detect both IgG and IgA levels.  

Methods 

Results

- Immune response significantly increases over time in the majority of patients, but 22% still showed no significant serological immune response after the 8-12 weeks. This result shows Immunity builds over time in some patients, but the 22% that did not show an immune response may not hold immunity and may be able to be reinfected. 
- Exposed individuals had no immune response both at baseline and follow-up, rejecting previous hypotheses that exposure without infection might cause a silent immune response. 
- The lack of immune response for the uninfected contacts reveals none of the hospital staff in the study contracted Covid-19 between the baseline and follow up while maintaining interaction with hospitalized covid-19 patients, highlighting the effectiveness of the PPE, distancing in the workplace, and hand-washing procedures that were used in this hospital system. 
- The decrease in IgA levels over time is consistent with previous studies suggesting IgA levels cannot be used to determine a long-term immune response.


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