So far this season there has been an unusually low level of influenza in Norway, but from week 10 the increase has been marked, says doctor Trine Hessevik Paulsen at FHI.
In week 12, influenza virus was detected in 1,179 people. The proportion of positive samples in week 12 was 11.4%.
The flu outbreak is underway
Since the proportion has crossed 10%, the flu outbreak is considered to be ongoing. The virus most commonly detected is an influenza A virus of the H3N2 subtype. This is a slightly changed version compared to the H3N2 viruses we have had in Norway before. It is therefore expected that the immunity of the population is lower against this variant than previous variants.
There has also been a significant increase in influenza admissions in parallel with the increase in influenza virus detection in recent weeks. In week 12, 136 influenza admissions have been registered so far, a number that is expected to increase somewhat in the coming days as the figures are updated.
An increase in the flu is unusual at this time of year. Normally, the flu epidemics are in full swing at this time. Unlike previous seasons, there has been almost no flu in circulation through the pandemic. The population’s immunity to influenza is therefore expected to be lower than normal. It is uncertain when the peak of the outbreak will be reached, and how extensive the flu outbreak will be. A further increase in influenza activity in the coming weeks is nevertheless likely. It is expected that public holiday periods such as Easter and the seasonal effect, as it is now rapidly approaching spring and summer, will put a damper on the spread of influenza.
There are far fewer who have been vaccinated for influenza than for covid-19 – also among the risk groups there are many who have not been vaccinated against influenza. This primarily applies to people under the age of 65 where vaccination coverage is below 40%, and especially children with conditions that increase the risk of serious illness, where approximately 8% have been vaccinated. Among those over 65, about 64% have taken the vaccine. Estimates from Denmark and France indicate that the vaccine has a moderate effect against infection among younger people under the age of 45 against the virus we see in Norway now. The effect among older people seems to be low. The vaccines probably have a slightly better effect against developing serious illness.
Early antiviral treatment for influenza is relevant for people at risk and in case of serious illness. Preventive treatment may be relevant in the event of an outbreak in a nursing home.
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