The nine most serious cases have seen flu patients end up in intensive care beds.
More than 2,400 people have also seen their GP with the symptoms so far this winter.
Dr Richard Roberts, head of the vaccine programme at Public Health Wales, said: "It's not too late to get vaccinated."
It comes as visits to GPs, hospital and intensive care admissions have all increased across Wales in the past few weeks.
Officials said flu will inevitably add to the burden on accident and emergency departments across many parts of Wales already dealing with existing winter pressures.
All age groups have been affected, although young children, the elderly and adults with chronic conditions are particularly vulnerable.
Dr Roberts added: "Recent figures suggest that flu is now circulating across Wales. Although those in risk groups should have been vaccinated by now, it's not too late to get vaccinated."
The vaccine protects against the most common H1N1 virus.
Influenza B viruses are also being detected, which usually affect younger people and children.
"From recent experience, we would expect that the flu virus will be circulating in Wales for six to eight weeks or even longer so it is important to ensure that remaining eligible people are vaccinated as quickly as possible," said Dr Roberts.
Cases of flu are rising in Wales with 51 patients treated in hospital since October, public health officials have said.