Flu Symptoms 2024 How Long Does It Last. Trivalent flu vaccines are formulated to protect against three flu viruses (an a. Symptoms can begin between one and four days after you’ve been exposed to the virus.

If you have symptoms of long flu, including shortness of breath and a lingering cough, and they last for more than two weeks after you recover from the flu, it’s time to consult a doctor. Flu symptoms usually appear two to three days after contact with the virus, according to the university of pennsylvania health system, but you may start to feel sick.