Flu RATES in Scotland remain low, but are above average for the time of year.
Surveillance for week 41 (week ending October 16) – officially considered the second week of UK ‘winter flu season’ – shows there were 133 lab-confirmed cases of influenza in Scotland, down from 122 in week 40.
Only a fraction of cases are detected by laboratory testing, but these data are used to estimate overall prevalence in the community.
Current estimates place the incidence rate of influenza at 2.4 per 100,000.
This is considered “low”, but compares to around one per 100,000 at the same time of year for the three years before the pandemic: 2017/18, 2018/19 and 2019/20.
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In each of those years, cases peaked between late December and early February, with flu rates peaking at 26 per 100,000 in 2017/18 – the last bad flu season.
It comes amid warnings that the UK could face a ‘twin outbreak’ of Covid and flu this winter, after two winters with virtually no flu following measures such as social distancing and masking introduced to curb the pandemic.
Flu rates in Scotland are currently low, but above average and rising (Source: PHS) (Picture: PHS)
The number of lab-confirmed flu cases in the past two weeks is almost equal to the peak in 2021/22 (Source: PHS) (Picture: PHS)
The number of laboratory-confirmed cases in Scotland in weeks 40 and 41 – at 155 in total – compares to around 20 in weeks 40 and 41 last year.
Influenza activity currently appears to be highest in Lanarkshire, where it fell from low to ‘moderate’ (5.1 to 14.7 per 100,000) in the most recent week.
However, regional estimates can be skewed by relatively small or large numbers relative to population size.
NHS Lanarkshire appears to have the highest flu rates currently (Source: PHS) (Picture: PHS)
The Public Health Scotland report says that while the number of cases is above average for the time of year, the number of people in hospital with flu is lower than in pre-pandemic years.
PHS notes that the number of flu-related hospitalizations in Scotland has increased since June.
At the start of the “flu season” in week 40, “there were 54 hospitalized patients who had tested positive for influenza”.
Of these, the majority (49) had influenza A, of an “unknown subtype”. This matches patterns already seen globally during the winter flu season in the southern hemisphere.
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The flu hospitalization rate in Scotland was one per 100,000 in week 40, rising to four per 100,000 in patients aged 75 and over.
PHS added: “The number of hospitalized patients who have tested positive for influenza reported so far this season is lower than the previous five seasons before the Covid-19 pandemic.”
The number of people hospitalized with the flu in the 2017/18 season peaked at over 1,000 and 500 in 2019/20.
However, the number of current flu hospitalizations is about five times higher than it was at the same time last year.
The number of patients in hospital in Scotland with a positive flu test is around six times higher than a year ago (Source: PHS) (Picture: PHS)
Compared to the same weeks in pre-pandemic years, the number of influenza patients in hospital remains relatively low (Source: PHS) (Picture: PHS)
As of October 16, more than 870,000 eligible adults have been vaccinated against the flu.
This included nearly 60% of over-65s and 83% of elderly residents of care homes, who were prioritized for inoculation.
Coverage is lower for other groups, ranging from just under 10% for clinically vulnerable 18-64 year olds and 16% of social workers, to 36.5% of health care workers.
The majority (94%) of people receiving a Covid winter booster who are also eligible for a flu shot received both vaccines at the same appointment.
The main strains of influenza circulating in the world over the past year are an unsubtyped form of influenza A (dark green) and influenza A(H3). This is similar to current patterns in Scotland (Source: PHS/WHO) (Image: PHS/WHO)
Meanwhile, the PHS report notes that in Australia – whose flu season is seen as a potential indicator for the UK – flu activity is now low after peaking in June.
Australia saw an early surge in cases from around April, but the infection-to-death ratio was lower than it had been during the 2017 flu season.
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Year-to-date, Australia’s cumulative notification rate for influenza nationwide is 875.4 per 100,000 population.
This exceeds levels seen in most pre-Covid years. For example, influenza rates ranged between 121.8 and 422.3 per 100,000 between 2011 and 2018, with the exception of 2017 which remains a peak year for influenza in Australia with a total notification rate of 1,021. 4 per 100,000 inhabitants.