Adults eligible for the flu jab are being urged to have the free vaccination as the “best defence” against the illness.
Latest figures show that the number of people suffering from flu in Scotland has more than doubled compared to the same period last year, increasing pressure on hospitals.
However, just over four in 10 (41%) of those aged under 65, who are considered “at risk”, have had their flu jab this winter.
The uptake level among pregnant women with other risk factors is 57.5% and 44% in pregnant women without other risk factors, Health Protection Scotland (HPS) data showed.
Health Secretary Shona Robison and the Chief Medical Officer (CMO) are joining together to urge all eligible adults to take up the offer of the free flu vaccination.
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Ms Robison said: “The flu virus can make even healthy people very unwell - and puts extra pressure on our health service at what is already a very busy time of year.
“The flu vaccine offers the best defence against the most common strains of the virus circulating this year and has an excellent safety record.
“Each year the World Health Organisation determines which influenza strains should be covered within the influenza vaccination programme and the health services across the UK use these recommended vaccines as these are likely to be the most effective.”
Around 46 Scots in every 100,000 were suffering from the virus during the last week in December 2017, up from 22 in every 100,000 for the same week in 2016, according to latest HPS figures.
Early testing also found that just over half of the circulating strains of flu match those in the 2017/18 vaccine.
The HPS report also highlights that around half of NHS boards are reporting significant ward pressure as a result of the virus.
CMO Dr Catherine Calderwood said: “Every year in Scotland, around two thirds of people who get severe flu and need intensive care treatment have a health condition such as chronic lung or heart disease.
“Given that we’ve already seen a large increase in cases of flu this winter, I’d encourage those who are eligible - including those with underlying health conditions, pregnant women and healthcare workers - to make getting the vaccination a priority and book an appointment with their GP practice or health board as soon as possible.”
Health experts said that anyone with a health condition is at greater risk from flu.
Over-65s, pregnant women and healthcare workers are also eligible for the free vaccine.
The Scottish Government said the in-school vaccination programme is achieving high levels of vaccination amongst primary school children, while the Childhood campaign this year focuses on encouraging parents of two to five-year-olds to have their child vaccinated.
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