Parents are being urged to get their children a flu jab within half a year as the NHS warns of a rise in cases.
It's early in the flu season, health officials say, and the latest figures for England show cases and hospitalizations are rising.
NHS England said many schoolchildren have already received the vaccine at school, but there are still options for those who have not yet done so, including pop-up clinics.
General practitioners' offices can vaccinate school-age children and children with certain medical conditions, as well as children two to three years old, against influenza, and preschoolers can also be taken to the pharmacy to get the vaccine.
Most children are offered the vaccine as a nasal spray rather than an injection.
NHS England's weekly flu and Covid surveillance report said influenza activity had increased, “particularly among children”.
Duncan Burton, England's chief nursing officer, said it was worrying that flu broke out earlier this year and the rise in children was “worrisome”.
“Flu can spread like wildfire through schools and can cause serious ill health for children,” he said.
“The virus changes every year, so vaccination remains the best way to protect your child from serious illness.”
He urged parents to make sure they agree to have their child vaccinated at school or to find a clinic near them.
The pop-up clinics were held in places such as bowling alleys and fire stations, Mr Burton told BBC Radio 4's Today programme, adding that the vaccine was “quick, simple and safe”.
Dr Fari Ahmad told BBC Breakfast that while she is monitoring cases, “I don't think we've reached the peak yet.”
“When it comes to influenza, it's a war we fight every year. The flu is unpredictable, it still kills people, and we try to vaccinate enough people every year so that when the big surge comes, we won't be wiped out,” she said.
Dr Ahmad said vaccinating enough school-age children meant it would improve this surge “because they are the spreaders”.
“It will be great for the kids individually, but it will also be better for all of us,” she said.
NHS England said the latest campaign has already delivered more than 10 million vaccines, including to almost 1.5 million school-age children and more than 300,000 eligible two and three year olds.
Free vaccines are available to people over 65, with certain chronic health conditions, pregnant, living in a nursing home, primary caregivers of an elderly or disabled person, or living with someone with a weakened immune system.
