In the first week of the year, 2,131 cases of influenza were detected, an increase of 22 percent compared with the last week of last year.
The spread of infection is assessed to be at a medium level, the Public Health Agency writes on its website.
Influenza A accounts for almost all confirmed cases, and the H3N2 strain is dominant.
The spread of the infection is expected to continue to burden the healthcare system.
Last week, 24 people with confirmed influenza were admitted to intensive care. The week before, that number was 28.
Last week, 39 people with confirmed influenza died, according to preliminary figures, compared to 51 the week before.
