For the moment, there have been a higher proportion of people falling ill in Norrland than in southern Sweden, but the number of cases is rising.
The number of infected people is expected to increase over the coming weeks and usually reaches its peak in January or February.
It's still too early for authorities to say which strain of the virus will dominate this season, but a majority (87 percent) of those affected so far have had influenza A, of which the most common type is also known as swine flu.
People who are pregnant, aged over 65 or have certain chronic conditions are advised to get a flu vaccine, which is offered everywhere in Sweden although the cost can vary by municipality.
“It takes up to two weeks to get protection from the vaccination, so it's high time to get vaccinated if it's not already been done,” Public Health Authority investigator AnnaSara Carnahan said in a statement.