EXPERTS have warned that there is "a lot of uncertainty" over the impact of flu on the health service this winter.

Although the virus is widely expected to make a resurgence after virtually disappearing during the pandemic, signals from Australia suggest that the major strains in circulation may be less deadly compared to previous winters.

The vaccine is also believed to be a "good match".

However, scientists also cautioned that waning immunity could result in a flu season "as bad as some of the previous bad years".

ANALYSIS: What can Australia's experience tell us about what to expect? 

Professor Sir Peter Horby, an expert in infectious diseases and director of the Pandemic Sciences Institute at Oxford University, said a lack of immunity due to prior exposure "means there may be slightly more transmission than usual and slightly more susceptibility to severe disease than usual".

The Herald: Professor Sir Peter HorbyProfessor Sir Peter Horby (Image: Oxford University)

He added: "There's certainly a lot of uncertainty but there is a possibility that we could have a worse season in terms of overall numbers of cases and potentially admissions to hospital.

"It may not be worse than previous years but there's the potential that it could be as bad as some of the previous bad years."

It comes as the latest data for Scotland shows that the current incidence rate, based on laboratory-confirmed cases, is low but around three times higher than normal for the time of year.

The Herald: Flu rates in Scotland are low, but significantly higher than average for the time of year. However, the increase appeared to level off at the end of OctoberFlu rates in Scotland are low, but significantly higher than average for the time of year. However, the increase appeared to level off at the end of October (Image: PHS)

The Herald: The number of people admitted to hospital who tested positive for flu is much higher in 2022 compared to October 2021The number of people admitted to hospital who tested positive for flu is much higher in 2022 compared to October 2021 (Image: PHS)

The number of cases detected last week - 183 - had barely changed from 187 in the previous week, however.

The number of hospital patients testing positive for flu - 88 in the week ending October 23 - compares to fewer than 10 at the same time last year but is "lower than that for the five previous seasons prior to the Covid-19 pandemic", according to Public Health Scotland.

READ MORE: NHS preparing for 'significant excess deaths' this winter 

In Australia, the influenza season took off much earlier than normal and peaked in June.

In total, its surveillance programme has reported 225,332 cases and 308 deaths since April, with a median age of 82.

However, the case-fatality ratio - the number of deaths reported for every known infection - is around half what it was in 2017, when 745 Australians died.

Scientists said it is unclear whether this indicates a milder virus, behavioural changes, or a lag in identifying flu's impact - for example through excess mortality.

The Herald: Australia experience record flu rates in May and June this year, but to total number of confirmed cases to date during 2022 is lower than it was in 2017 - Australia's record flu season by infection numbersAustralia experience record flu rates in May and June this year, but to total number of confirmed cases to date during 2022 is lower than it was in 2017 - Australia's record flu season by infection numbers (Image: Australian Government)

Dr John McCauley, who was until the end of September this year the director of the WHO Collaborating Centre for Influenza at the Francis Crick Institute, said colleagues in Australia had described the 2022 flu season as "moderate".

"Other indicators rather than just the numbers of cases were not particularly high," he said.

The Herald: Dr John McCauley Dr John McCauley (Image: Francis Crick Institute)

"The number of cases were higher. I don't know if that was due to testing - it wasn't over-testing, just more testing. But the number of deaths was low.

"Bear in mind though that counting excess deaths is not a trivial thing.

"It usually takes some months before you retrospectively work out how many winter deaths there were."

Dr McCauley added: "The feeling was that the elderly were doing some voluntary isolation off the back of corona, so they weren't really exposing themselves to the risk of infection so much."

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Prof Horby said the severity of any flu season is "very hard to predict".

He said: "Obviously it's the elderly who are at most risk of severe disease, and it may be that a smaller proportion [of elderly adults in Australia] were exposed than in previous years.

"It can also depend on levels of vaccine coverage, the match between the vaccine and the circulating strain, and how that strain relates to previous exposures.

"So it is very difficult to predict."