More evidence is being gathered about serological response to SARS-CoV2 virus revealing more about how antibodies can complement PCR in SARS-CoV2 diagnostics. In a new study published in Nature, serological response was studied.
In summary, most patients with COVID-19 infection generated serological response within few weeks from the onset of symptoms. 100 % of patients had detectable IgG antibodies against SARS-CoV2 within 19 days after symptom onset, and more than 50 % had detectable IgG already within the first 5-7 days. Following the serological courses in subset of patients revealed that the highest antibody titers were reached in about 6 days for both immunoglobulin types. Seroconversion of IgG and IgM occurred simultaneously or sequentially with either type preceding.
It was also shown that serology can complement PCR testing for asymptomatic and suspected persons with negative PCR results. Serology could identify 4 out of 52 suspected COVID-19 patients with several negative PCR results that were concluded as COVID-19 positives with high probability. In addition, serological assessment could correctly identify infected close-contacts of COVID-19 patients that were PCR positive, and additional persons that were PCR negative (4,3%). 10 % of these seropositive persons were asymptomatic.