Just How Effective are Flu Shots?

Each year, the public is encouraged to receive a seasonal influenza vaccine, but the level of protection it provides varies from year to year. A report published in JAMA (2013; 309(24): 2557–2558) reviewed the effectiveness of influenza vaccination in healthy adults and found an average effectiveness of about 59%.

The analysis, led by Michael Osterholm of the University of Minnesota, examined 31 comprehensive studies assessing influenza vaccine efficacy. The authors noted that earlier estimates from public health agencies had suggested vaccine effectiveness in the range of 70–90%, but that these higher figures were not consistently supported by high-quality evidence.

One of the key concerns raised in the report was the lack of strong data in the populations most vulnerable to influenza complications. Despite children and older adults being at the highest risk, the authors found a surprising lack of modern, high-quality trials evaluating vaccine effectiveness in children aged 2–17 or adults over age 65.