Wakefield has the highest levels of flu in Yorkshire, according to figures from GP consultations.
Latest statistics, which record GP appointments for flu-like illnesses, show Wakefield had a rate of 124.7 consultations per 100,000 people.
* Click here to sign up to free news and sport email alerts from your YEP.
That compares to 71.5 for Leeds and 67.8 for Kirklees in the figures up to December 27 which are an indicator for health experts and do not take account of the majority of people who recover at home without seeing their GP.
* Click here to follow the YEP on Twitter.
NHS bosses reiterated their advice for those eligible to get their free flu jab, which protects against both seasonal and swine flu.
Dr Andrew Furber, director of public health for NHS Wakefield District, said: "Now the bank holidays are over, I urge people in at-risk groups such as those with chronic conditions such as heart and kidney disease, asthma and diabetes, the over 65s and pregnant women to make an appointment with their doctor as soon as possible.
"For most healthy people, flu remains an unpleasant but mild illness and generally they will recover in a few days after getting lots of rest, drinking plenty of fluids and using over-the-counter remedies such as paracetamol."
The warning comes after a top doctor spoke of his fears that the flu outbreak could become much worse as youngsters returned to school today.
Professor Steve Field, left, former chairman of the Royal College of GPs, said it would be "when people start to go back to work and to school that we will, I suspect, see the sharpest rise, when we will really see this become the children's epidemic."
Since October, 39 people have died with flu, including 11 youngsters under 15.
Paul Johnstone, NHS Yorkshire and the Humber regional director of public health, added: "People in 'at risk' groups are more likely to develop complications if they catch flu, and the seasonal flu jab will not only protect them, it will also protect their families and the people around them."
Contact your GP for jab advice.