The Health Information and Quality Authority has published its evidence review behind the decision to reduce the incubation period for people who test positive in the community for Covid-19 from 14 days to ten.
It examined 15 international studies.
Dr Máirín Ryan, HIQA deputy CEO, said that from the evidence, it found that patients with mild to moderate Covid-19 disease are unlikely to be infectious beyond ten days from their first symptoms.
However, she said that some limited evidence from a small number of studies found that patients with severe-to-critical symptoms and those who are immunocompromised may be infectious for 20 days or more.
HIQA said the evidence summary focused on evidence relevant to those with Covid-19 and had no impact on the duration of quarantine for close contacts of confirmed cases, household contacts of people with symptoms of the virus and people arriving into Ireland from a non-green list country.
These people must restrict their movements for 14 days.
The World Health Organization says data to date suggests 80% of Covid-19 infections are mild or asymptomatic, 15% are severe infection, requiring oxygen and 5% are critical, requiring ventilation.
Generally, you need to be 15 minutes or more in the vicinity of an infected person and within two metres of them, to be considered at-risk, or a close contact.