Flu Shots Less Than 50% Effective

During the 2022–2023 influenza season in the United States, the highest influenza-associated pediatric hospitalization rate was reported in a decade.

To understand this uptick in cases, researchers published a Major Article on November 16, 2023, focused on acute respiratory illness-associated emergency department or urgent care (ED/UC) encounters or hospitalizations among those six months–17 years during October 2022–March 2023.

This U.S. CDC-funded analysis estimated influenza A vaccine effectiveness (VE).

Among ED/UC patients, 15.2% of influenza-positive versus 27.1% of influenza-negative patients were vaccinated. The VE was 48% (95% confidence interval [CI], 44%–52%) overall, 53% (95% CI, 47%–58%) among children aged six months–4 years, and 38% (95% CI, 30%–45%) among those aged 9–17 years.

Among hospitalizations, 17.5% of influenza-positive versus 33.4% of influenza-negative patients were vaccinated; VE was 40% (95% CI, 6%–61%) overall, 56% (95% CI, 23%–75%) among children ages six months–4 years and 46% (95% CI, 2%–70%) among those 5–17 years.

These researchers concluded vaccination against seasonal influenza remains the most effective public health strategy to protect against influenza illness and severe complications and that during the 2022–2023 influenza season, vaccination reduced the risk of influenza-associated ED/UC encounters and hospitalizations by less than half (overall VE 40–48%). 

Previous Flu Shot Effectiveness studies are posted at Precision Vax.