vaccine for covid 19..

COVID-19 testing involves analyzing samples to assess the current or past presence of SARS-CoV-2. The two main branches detect either the presence of the virus or of antibodies produced in response to infection.[1][2] Tests for viral presence are used to diagnose individual cases and to allow public health authorities to trace and contain outbreaks. Antibody tests instead show whether someone once had the disease. They are less useful for diagnosing current infections because antibodies may not develop for weeks after infection.[3] It is used to assess disease prevalence, which aids the estimation of the infection fatality rate.