Seroconversion assessed by different methods:
90.9% (30 of 33) SARS-CoV-2-positive patients in the convalescent phase
(> 21 d after onset of the symptoms) tested had
seroconverted at T1 in April and in total, 85.3% of the patients (29 of
34 samples) had seroconverted until September, as determined by
neutralization test (table 1).
Overall, 85.3% of SARS-CoV-2-infected persons
seroconverted and maintained
constant neutralizing antibodies over the study period of five months.
The highest number of positives was found in the IgG IFA one month post
infection (32 of 34; 94.1%), the lowest number of seroconversions was
found in CLIA IgG (28 of 34; 82.4%). In 11 cases (32.4%), IgM was
detectable by IFA 28 – 41 days after onset of the symptoms.
Four patients had no specific antibody response at all and eleven
patients developed only weak antibody responses five months post
infection. All four negative patients had a mild course of disease;
their mean age was 51 (sd = 12.4) years.
Comparison CLIA IgG – ELNA
Both methods showed that specific antibodies stayed constant over the
observation period and that a stronger disease severity led to a more
stable antibody response.
CLIA IgG recognized two sera from the first time point as positive
(5.9%), which turned out as negative in ELNA. This result goes along
with the manufacturer´s information concerning 95% specificity and 0%
false-negative results. Repeated serologic investigations at T5
exhibited one patient (3.0%) false-negative in CLIA IgG.