By Ethan Covey
Influenza vaccines provided moderate protection against laboratory-confirmed influenza during the 2023-2024 flu season, according to an analysis of state-level California surveillance data.
The California Department of Public Health (CDPH), working with the CDC, calculated interim influenza vaccine effectiveness (VE) estimates against laboratory-confirmed influenza using public health data from October 2023 through January 2024 (MMWR Morb Mortal Wkly Rep 2024;73[8]:175-179).
From Oct. 1, 2023, through Jan. 31, 2024, a total of 678,422 influenza laboratory test results meeting study inclusion criteria were reported to CDPH, including 77,501 (11%) positive and 600,921 (89%) negative test results. Twenty-eight percent of people had documented receipt of the 2023-2024 influenza vaccine, including 18% of those who tested positive and 29% who received a negative test.
The overall adjusted VE was 45% against receiving either a positive influenza A or B result, 42% against a positive influenza A result, and 76% against a positive influenza B result.
VE was highest among people aged younger than 18 years, and declined with age, falling to 30% among adults 65 and older.
“Reporting of influenza laboratory data and immunization records to public health offers jurisdictions an opportunity to calculate timely estimates to better inform local influenza prevention efforts,” said Sophie Zhu, PhD, an infectious disease epidemiologist with the CDPH and a CDC Epidemic Intelligence Service officer, and the lead author of the report.
Dr. Zhu noted the importance of surveillance data to track effectiveness of seasonal vaccines.
“Timely surveillance data can allow for more rapid calculation of interim influenza vaccine effectiveness,” she said. “Early VE estimates could be used to communicate the benefits of vaccination to the public and thus incentivize and support vaccination efforts.”
