With the upsurge in number of COVID-19 patients during the fifth wave mainly due to Omicron variant in Hong Kong [22–24], we here reported the use of one-step real-time RT-qPCR on nasopharyngeal specimens to investigate the role of nasopharyngeal expression of MPO, ADA, CCL22, TNFα, and IL-6 messenger RNA (mRNA) in the diagnosis of COVID-19. The gene discussed is ADA; the disease is COVID-19.