To evaluate the sensitivity of COVID-19 NP-IgA ELISA, the levels of SARS-CoV-2-specific NP-IgA antibodies were measured in sputum (n = 28), throat swabs (n = 28), and serum specimens (n = 28) of COVID-19 patients 15–21 days after infection. The gene discussed is CD79A; the disease is infection.