From https://www.ecdc.europa.eu/en/seasonal-influenza/facts/questions-and-answers-seasonal-influenza https://www.ecdc.europa.eu/en/seasonal-influenza/facts/ques

From https://www.ecdc.europa.eu/en/seasonal-influenza/facts/questions-and-answers-seasonal-influenza https://www.ecdc.europa.eu/en/seasonal-influenza/facts/quest... > The infectious period varies a bit from person to person but it is considered that an adult with flu starts being able to pass on the infection from during the day before their symptoms appear and then they remain potentially infectious for three to five days. The start is probably the same for children but it is often stated that it runs on for up to seven days after onset. > However, the risk to others is not constant throughout. Infectiousness rises steeply when the person starts feeling unwell and that is when he or she is most dangerous to others. The risk of catching influenza from someone even just before they become ill and after the end of the first three days is quite low.