Retail flu vaccinations in the U.S. by flu season

Flu shots—which take one to two weeks to be fully effective—were lagging through September compared with recent years.

July-August    September
October            November
December        January-February

Vaccination data are collected weekly; weeks that straddle two months are grouped with the month that accounts for the majority of days in that week.

Chart: Emily Barone Source: IQVIA