Furthermore, it has been stated that salivary testing is the most convenient way to measure IgA, the reason by which it has been used to characterize mucosal immune responses to many viral infections such as SARS, MERS, influenza, HIV, and RSV. Serum IgA has been detected in COVID-19 patients and appears to be detectable earlier than IgM or IgG antibodies, possibly as early as two days after onset of symptoms, suggesting that IgA may be the first antibody to appear in response to SARS-CoV-2 infection47. This evidence concerns the gene CD40LG and COVID-19.