Covid Scotland: Almost no flu cases despite fears of post-lockdown resurgence

Figures from Public Health Scotland show a "marked decrease" in flu compared to pre-Covid winters, with just four cases confirmed by laboratory testing out of nearly 5000 patients swabbed in the week to January 16.

GP consultations for influenza-like illness - which in a 'moderate' flu season range from around 40 to 100 per week for every 100,000 people - are running at less than one per 100,000.

It comes despite modelling by the Academy of Medical Sciences which projected anything from 15,000 to 60,000 flu deaths across the UK this winter with lockdown restrictions gone, and warnings from England's deputy chief medical officer Professor Sir Jonathan Van-Tam that a lack of population immunity posed a “significant public health concern”.

Barely any flu cases are being detected in Scotland for the second winter in a row

PHS points to Covid mitigation measures "such as social distancing and improved hand and respiratory hygiene, including the wearing of face masks" for decreasing transmission.

However, Professor Jürgen Haas, head of infection medicine at Edinburgh University, notes that rates of other respiratory viruses - such as human metapneumovirus (HMPV), respiratory syncytial virus (RSV) and parainfluenza - had returned to similar or above average levels for the time of year.

He said it was "hard to explain" why influenza had all but disappeared.

"We have hardly any cases of flu here in Edinburgh - the flu incidence is really very low, similar to last year. But last year we also tested [for influenza] much less.

"This year it's a bit different because we did start to test for the other respiratory viruses again - we almost tripled the number of people that work in virology here at the Royal Infirmary of Edinburgh.

"Up to now we have hardly seen any flu cases this season, but what we did see was quite a lot of MPV and RSV.

"That means that restrictions like mask wearing and so on cannot, in my opinion, really be a good explanation for why we see so little flu. Otherwise the RSV and MPV infections should have been prevented as well."

Cases of parainfluenza have been higher than previous years at the end of 2021 and beginning of 2022 (red line)

Rates of HMPV were well above previous years at the end of 2021 (red), only falling as Omicron drove a reduction in social contacts

RSV rates soared out of season last August (green)

Rates of rhinovirus exceeded previous years in late 2021, only declining at the start of 2022 following Omicron-related restrictions (Source: all Public Health Scotland)

The rise of Omicron during peak flu season - and subsequent reductions in social interaction - may have blunted influenza's opportunities to spread, but Prof Haas said he would be surprised if an easing of restrictions now led influenza to rebound.

He said: "Usually the influenza season ends around April, so I think it's unlikely we will see a large number of flu cases later on in the Spring.

"That would be rather unusual as the main season is really January and December, and now we at at the end of January so I would say the danger is probably low."

In England and Wales, flu rates are slightly higher - around 0.6% of patients tested are positive compared to 0.1% in Scotland and Northern Ireland - but that is still far below an average winter.

Globally, influenza cases are also low, but increasing - especially in milder regions of the northern hemisphere.

Between December 6 and Boxing Day, the WHO's Global Influenza Surveillance and Response System (GISRS) laboratories tested more than 522,595 specimens and identified 27,153 cases of flu - a positivity rate of 5%.

Flu cases have been rising globally since November

Around three quarters of samples were influenza type A, of which more than 95% belonged to the H3N2 strain.

Significantly, flu seasons dominated by H3N2 activity are typically more severe, particularly for elderly adults and young children.

In Scotland, 90% of adults over 65 and around 60% of pre-school children, aged six months to five years, have had the winter flu vaccine, but it is still unclear how protective it is against the types of influenza in circulation this year. 

This has led to caution from health leaders in Europe not to rule out a threat from flu just yet.

Last week, the European Centre for Disease prevention and Control (ECDC) warned that influenza has returned since mid-December at a faster-than-expected rate.

In the final week of December there were 43 flu patients in intensive care across the region, compared to one during the whole of December 2020.

A number of European governments, including Spain, are pushing for an end to restrictive Covid measures including border controls and isolation in favour of treating the coronavirus "as an endemic illness", like flu.

But Pasi Penttinen, the ECDC's top flu expert, said lifting all remaining measures could end up prolonging the flu season in to summer.

He said: "If we start to lift all measures, the big concern I have for influenza is that, because we have had such a long time of almost no circulation in the European population, maybe we will shift away from normal seasonal patterns."

A "twindemic" of flu and Covid could put excessive pressure on already overstretched health systems, said the ECDC.

In France, three regions - including the Paris region - are already facing a flu epidemic, according to the French health ministry. Others are in a pre-epidemic phase.

So far this winter France has recorded 72 serious cases of flu, and six deaths.