Two patients have died from influenza in the past week, as cases and hospitalisations involving the virus increased significantly.
Notifications of RSV (respiratory syncytial virus) also rebounded, defying hopes that this illness, which particularly affects young children, might have peaked for the winter.
So far this winter, six flu deaths have been recorded, according to the latest update from the Health Protection Surveillance Centre.
With a big increase last week in the number of over-65s attending GPs with flu-like symptoms, this winter is starting to resemble the bad flu season recorded in 2019/20, just before the start of the Covid pandemic.
The number of flu cases notified during the week increased to 370, well up on the 222 reported the previous week.
RSV notifications also increased, to 678, from 610 the previous week; half of these cases were under-5s and one-quarter were over-65s. The number of patients hospitalised with RSV was 239.
There were 123 hospitalisations for flu, almost double the number recorded in the previous week. The vast majority involved type A.
The HPSC says influenza is not circulating in Ireland and antivirals should be used for the treatment of at-risk groups, as well as prophylactically.
So far this winter, 15 flu patients have been admitted to critical care, including two in the last week.
Nine flu outbreaks were reported last week, six of them in hospitals. There were also four RSV outbreaks in nursing homes and hospitals and one outbreak involving a rhino/entero-virus.
Meanwhile, the HPSC says it is working closely with international partners, including the UK, in relation to recent detection of Grp A strep infections. An invasive form of Group A streptococcal infections has been implicated in the deaths of two children, one in Dublin and one in Belfast, in the past week.
A spokeswoman said the HPSC was considering the emerging epidemiological picture and all available evidence to inform its ongoing practice and guidance.
The prophylactic use of antibiotics is also considered in response to outbreaks as part of the risk assessment made by local public health teams, she said. The spokeswoman did not indicate whether any decision has been made to deploy antibiotics in this way.
Fifteen children under the age of 15 have died in the UK from invasive strep A illness, latest figures show.
