Flu Shots About 41% Effective

Influenza vaccines have provided moderate yet crucial protection against laboratory-confirmed influenza, outpatient visits, and hospitalizations for the past few decades.

Although influenza vaccine's effectiveness does vary based on virus type and age group, healthcare providers have emphasized the need to tailor vaccination strategies for those at the most significant risk.

A recent systematic review, meta-analysis, and meta-regression of test-negative design studies published in the journal Vaccines on February 28, 2024, provided a comprehensive evaluation of the seasonal influenza vaccine effectiveness (IVE) from January 2017 to December 31, 2022.

These researchers included 191 studies in their meta-analysis and found that the pooled IVE was 41.4% (95% CI: 39.2–43.5%) against any influenza.

The pooled IVE was 39.2 % (95 % CI: 36.5–41.9 %) in preventing influenza-associated outpatient visits and 43.7 % (95 % CI: 39.7–47.4 %) in preventing influenza-related hospitalization.

The IVE against any influenza was 48.6 % (95 % CI: 44.7–52.2 %) for children aged < 18 years, 36.7 % (95 % CI: 31.9–41.1 %) for adults aged 18–64 years, and 30.6 % (95 % CI: 26.2–34.8 %) for elderly aged ≥65 years.

The meta-regression revealed that the IVE was associated with the average age of study participants, in which both young adults [relative odds ratio (ROR) = 1.225, 95 % confidence interval (CI): 1.099–1.365, p = 0.0002] and elderly (ROR = 1.245, 95 % CI: 1.083–1.431, p = 0.002) manifested a significantly decreased effectiveness compared with children.

To better understand flu shot effectiveness during the current season, the U.S. DoD presented 'Influenza Surveillance and Mid-Season Vaccine Effectiveness' at the U.S. FDA vaccine meeting on March 5, 2024. 

The DOD calculated the Beneficiary VE for the 2023-2024 Mid-Season Influenza Estimates, which ranged from 43% to 53%.

Previously, the U.S. CDC emphasized annual immunization for those at the highest risk, both early in the flu season and even in late winter.

As of February 24, 2024, the U.S. CDC reported over 158 million flu vaccines had been distributed during the 2023-2024 season.

The national vaccination coverage estimates for the 2023-24 season as of February 17, 2024, for all adults, including Puerto Rico, was 47.8%, and coverage among states and Washington DC ranges from 38.6% to 59.6%.

Various types of flu shots (egg, cell, nasal) remain available at most clinics and community pharmacies through early Spring 2024.