Latent period (epidemiology)

Moreover, at a certain point in time after infection, the host becomes capable of transmitting pathogens to others, i.e. they become infectious or communicable.

The duration of the infectious period depends on the ability of the infected host individual to mount an immune response.

In COVID-19, the infectious period begins approximately 2 days before the onset of symptoms and 44% of the secondary infections may happen during this pre-symptomatic stage.

[5] In these kinds of cases with a significant number of pre-symptomatic (asymptomatic) transmissions, symptomatic surveillance-based disease control measures (such as isolation, contact tracing, enhanced hygiene, etc.)

are likely to have their effectiveness reduced, because a significant portion of the transmission may take place before the onset of symptoms and this has to be taken into account when designing control measures.

For example, even though HIV/AIDS has a very low transmission potential per sexual act, its basic reproduction number is still very high because of its unusually long infectious period spanning many years.

[1] From the viewpoint of controlling an epidemic, the goal is to reduce the effective infectious period either by treatment or by isolating the patient from the community.

[1] Since the precise moment of infection is very difficult and almost impossible to detect, the generation time is not properly observable for two successive hosts.

Generally, in infectious disease statistics, the onset of clinical symptoms for all the hosts are reported.

[10] Doctors and medical journals may speak of "latent" tumors, which are present but not active or causing symptoms.