For the first time this flu season, Health Protection Scotland (HPS) reported that there had been deaths linked to flu in patients who had been admitted to intensive care with the infection.
A total of 14 patients have received intensive care treatment due to flu, with four of these dying as a result.
However, the number of people seeing their GP with flu-like symptoms remains low for this time of year, HPS said.
Experts urged people in at-risk groups, such as the elderly and those with conditions such as asthma, to get vaccinated to protect themselves.
HPS said that so far their surveillance data revealed low levels of flu activity, but a rising number of severe cases showed that the infection was circulating in the community.
The agency said that the H1N1 strain, which caused the swine flu pandemic of 2009, had been the predominant strain detected in laboratory confirmed flu cases this winter.
All but one of the 14 cases treated in intensive care were identified with the swine flu strain, it said.
HPS said that death rate among those admitted to intensive care with flu remained similar to previous years, despite the smaller number seen so far this winter.
The four deaths out of 14 severe cases seen this year means a death rate of 28.6 per cent. In winter 2012/13, the 37 deaths out of 128 severe cases gave a fatality rate of 28.9 per cent.
Dr Syed Ahmed, from HPS, said: “Vaccination offers the best protection for those at high risk from seasonal influenza. These groups should have received their vaccine by now, but it’s never too late to contact your GP to arrange for vaccination.”