The period when the infected individual can transmit the infectious agent is known as the infectious period , and it does not necessarily begin from the point of infection. The period before a case becomes infectious and when it cannot transmit the disease is called the 'pre-infectious' or 'latent' periods. The diagram below illustrates these concepts.

For COVID-19, the incubation period is the period from exposure to the Virus to symptom onset, usually 5–6 days, but can be up to 14 days. During this period, also known as the 'pre-symptomatic' period, the infected individuals can be contagious and transmit the Virus to healthy individuals in the population.

Finally, there is a category called "Asymptomatic," which includes infected and contagious (can transmit the infection) without having clinical symptoms and that can be found among the fully vaccinated people.