When Should You Get a Flu Shot? Posted on September 3, 2026September 4, 2026 For most people, September and October are good times to get a flu shot. San Mateo County Health is offering free flu vaccine clinics this fall. If you miss the early fall window, vaccination may still be beneficial later in the season while flu viruses are circulating. Give wellness your best shot Find a free flu vaccine clinic View upcoming clinic dates, locations and hours and find one that works for you. View the clinic schedule