Covid virus orbit CGI.  A virus is a submicroscopic agent that replicates only inside the living cells of an organism. Viruses interact with all life forms, from animals and plants to microorganisms, including bacteria and archaea.  Most viruses use endocytosis to enter the host cell.  A key step in COVID‐19 pathogenesis is the entry of the SARS‐CoV‐2 virus into the airway epithelial cells. Since the COVID-19 pandemic began, the continuous evolution of this infectious disease has led to variations and mutations.  The Alpha variant was found United Kingdom in September 2020. The Beta variant was discovered in South Africa in December 2020.  The Delta variant was found in India in October of 2020.  The Omicron variant was found in multiple countries in November 2021 and has over 50 mutations. A vaccine roll out and physical distancing has been advised to prevent the spread of these infectious diseases. When a person is vaccinated against a viral or bacterial infection, a healthy immune system makes antibodies against one or more components of the virus or bacterium.  Exposure to the virus provides some immunity for at several months a Public Health England study has found.  However people may still carry the virus in their nose and throat and therefore have a risk of transmitting to others.