"We can already call this a flu epidemic," THL researcher Niina Ikonen told Yle on Tuesday.
Three types of virus are now spreading around the country: a B virus, an A virus known as H1N1pdm09 - better known as swine flu - and the H3N2 virus, which has recently been raging in the New York area.
Before Christmas, a few cases were recorded per week. Now at least 20-30 new cases reported weekly. Actual levels of illness may be significantly higher.
So far about 350 cases are on the books, roughly half of them influenza A.
"We don't know yet which of these viruses will be dominant this season," says Ikonen.
Hanna Nohynek, the head of the THL's Vaccine Programme Unit, says it is still worthwhile getting the influenza vaccine, since last winter's shots are no longer effective.
The THL recommends flu jabs for those over the age of 65, the chronically ill, expectant mothers and children under the age of three. The shot begins to give protection within a couple of days, reaching its full strength within two weeks.
Nasty stomach bug also at large
This is shaping up as a rough flu season because there are different viruses circulating, says Risto Pietikäinen, the chief physician for infectious diseases at Carea - Kymenlaakso Social and Health Services.
He expects the flu season to peak in February, around the time when Finnish schools have their winter ‘ski holiday’.
While influenzas A and B are just beginning to appear in Kymenlaakso, norovirus infections have also been proliferating for a couple of months. This bug can cause diarrhoea, nausea and vomiting.
“When the norovirus really strikes, we’ll have a shortage of beds in our central hospital,” Pietikäinen predicts.
The norovirus is spread by droplets, so he stresses the importance of careful hand hygiene. He notes that handshaking has been banned at the main Kymenlaakso hospital in an effort to slow the spread of the illness, and he recommends that all health centres adopt the same practice.