The flu vaccine is so far proving more effective in children than in adults in the UK, mid-season figures suggest.
The nasal spray flu vaccine is 87% effective in children aged two to 17 against the main circulating flu strain, influenza A(H1N1)pmd09, Public Health England data indicates.
Meanwhile, the flu vaccine is 39% effective against the same strain in adults aged 18 to 64.
No data is yet available for the over-65s or for other flu strains.
The data shows that more children than ever are being vaccinated, although take-up is lower in younger age groups.
The figures are preliminary and are subject to being revised by the end of the flu season in May, when more data is available.
Some 43% of two-year-olds have been vaccinated, compared with 45% of three-year-olds.
Among school-aged children, 56% to 64% have been vaccinated, depending on the year group.
Last year's final figures for the whole flu season of 2017-18 showed that the vaccine was only 15% effective among all age groups.
This included effectiveness of about 27% in children aged two to 17, 12% among people in at-risk groups aged 18 to 64, and 10% in those aged 65 and over.
For this latest flu season, a new "booster" vaccine has been brought in to improve effectiveness among the over-65s.
Dr Mary Ramsay, head of immunisation at PHE, said: "It is encouraging to see that this year's vaccines are offering a high level of protection against the main circulating strain of flu - particularly for children.
"Children tend to be 'super-spreaders' of flu and so protecting them is crucial for protecting the rest of the population.
"We're pleased that more parents have been taking up the offer of vaccination for their children and encourage anyone who is eligible to do so every winter.
"It's the best defence we have against this unpredictable virus."
Health Secretary Matt Hancock said: "The most basic instinct for any parent is to do whatever they can to protect their child. Vaccinations save countless lives and are absolutely vital.
"More children have been vaccinated this year to protect against flu and it is a positive sign that the vaccine itself appears to be more effective than in previous years.
"Our world-leading vaccination programme saves lives and I urge all parents of young children to make sure their child is vaccinated against flu and other childhood diseases."