**2.5 Rapid diagnostic test based on detection of antigens**

Since antigen tests are simple to perform, they are in high demand for COVID-19 diagnosis. For the evaluation of serious infections in samples, the novel rapid antigen detection test (RADT) is used. This test looks for and detects antigens generated by the SARS-CoV-2 virus in a sample taken from a person's respiratory tract [31, 32]. If adequate concentrations of target antigens are present in the sample, it will merge with particular antibodies fixed on a paper strip attached to a plastic casing within 30 minutes, using either visual or visible. Since the antigens found in the body are only released while the virus is actively replicating, such tests are the best used to detect acute or the early infection. This test depends on factors such as quantity and quality of virus collected from the person's body, duration from onset of one's illness, reagent formulation in a test kit. The test is cost effective, determines results in minutes and reveal an actively infection. They are already being used for influenza, HIV, tuberculosis (TB) and other infectious diseases [33, 34]. Due to the limited data availability for this test currently WHO does not recommend the antigen test keeping in mind the patient's health but encourages more research under this field.
