The flu shot's overall effectiveness during the 2018-19 season was 29 percent, according to CDC data provided to Becker's.
Health experts presented the flu season data June 27 at a meeting for the CDC's Advisory Committee on Immunization Practices.
Four things to know:
1. The CDC estimated the flu shot prevented between 40,000 and 90,000 hospitalizations this season.
2. The vaccine also reduced the risk of H1N1 illness by 44 percent in outpatient settings and by 60 percent in inpatient settings.
3. However, the CDC said this season's flu shot formulation offered "no significant protection" against illnesses caused by H3N2 flu strains. As a result, the U.S. saw a second wave of flu season in early March, reports PBS.
4. The CDC noted these estimates are preliminary and only account for data through May 2019. The agency will release an updated estimate once final data are available.