Antibody responses to SARS-CoV-2 in patients with COVID-19
Main result
No binding between SARS-CoV-2 antibodies and the S (Spike) protein from SARS 2002.
Cross reactivity between SARS-CoV-2 antibodies and the SARS 2002 nucleocapsid.
Seropositivity of SARS-CoV-2 antibodies:
-IgG 100% reached 17 to 19 days after symptoms onset. Plateau and positivity reached during the first 7 days.
-IgM 94,1% reached 20 to 22 days after symptoms onset, with a decrease after 3 weeks.
- IgG and IgM titers were higher in the severe group but no link found between IG titers and clinical features.
In the cohort of 63 patients followed up with blood tests every 3 days, seroconversion reached 96.8% after approximately 13 days.
With 23 patients followed, 3 different seroconversion profiles appear:
- IgM before IgG (9 patients)
- Synchronous IgM and IgG (7 patients)
- IgM after IgG (10 patients)
Taking into account MERS diagnosis, 70.7% were diagnosed with SARS-CoV-2 : 21/41 with initialy positive IgG, 8/18 with a factor 4 increase of their IgG titers.
To evaluate the help in diagnosis : 52 patients with suspected COVID ( both clinical and symptomatic) but with 2 negative RT-PCR, 4 patients presented with a seroconversion thus considering them positive.
To evaluate the role of serology testing: 164 "contact " patients, 16 with both RT-PCR and serology positive, 148 patients with a negative RT-PCR and 7 of them presented a seroconversion, showing that 4.1% of diagnosis would have been missed if only RT-PCR was used as a diagnosis tool.
Takeaways
Serology tests for SARS-CoV-2 to be use as a complement of the RT-PCR for:
Diagnosis (observable in the early stage of infection and fast results which is important to isolate infected patients)
Follow up of asymptomatic patients and "contact-cases"
Strength of evidence Moderate
Cohort study
Multiple objectives
Good methodology
But:
- small sample size, especially for severe condition
- no study of neutralizing antibodies
Objectives
Method
Cohort transversal study, multicentric
Numerous sub-studies:
1. To evaluate antibodies kinetic:
285 patients (RT-PCR positive), 39 with a severe or critical condition but only 70 with sequential sampling.
63 patients were sampled every 3 days.
2. To evaluate the use of a similar diagnosis definition than for MERS (diagnosis if IgG positive or if IgG increase of a factor 4 between two analysis).
Sampling should adhere to conditions:
-First sampling done during the first 7 days on the illness (n=34)
-First sampling done during the first 7 days on the illness but with negative IgG titer (n=1)
-Second sampling after 2 to 3 weeks
3. To evaluate the role of serology testing in diagnosis: 52 patients symptomatic or with abnormal radiographic findings but with two negative RT-PCR
4. Serologic surveillance of "contact"cases in couples : 164 patients with RT-PCR and serology.
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