ST. LOUIS (KTVI) – The flu season has hit the St. Louis area and urgent cares have seen a huge uptick in potential flu cases. One urgent care has seen around 400 possible cases of flu. But some doctors are concerned over the type of flu shot the public is getting. Flu shots are based annually on forecast for next year’s flu strains and vaccines are made based on the information. If the guess is wrong, the vaccine manufactured for the flu season is less effective.