Current Influenza Vaccine Effectiveness
I cannot provide a definitive answer about "this year's" flu shot effectiveness because the evidence provided does not contain current-season data, and vaccine effectiveness varies significantly from season to season based on the match between vaccine strains and circulating viruses.
What We Know About Influenza Vaccine Effectiveness in General
Influenza vaccine effectiveness depends critically on the antigenic match between vaccine strains and circulating viruses, with effectiveness ranging from 16% (not statistically significant) in poorly matched seasons to 70-90% in well-matched seasons among healthy adults under 65 years. 1, 2, 3
Recent Season-Specific Data Available
The most recent effectiveness data in the evidence shows substantial variation:
2022-23 season: VE was 54% against medically attended outpatient illness and 71% against symptomatic influenza A in children/adolescents, with good antigenic match between vaccine and circulating A(H3N2) and A(H1N1)pdm09 viruses 2
2021-22 season: VE was only 16% (not statistically significant) against A(H3N2) viruses, meaning vaccination did not significantly reduce risk of outpatient illness that season 1
2016-17 season: VE was 48% overall, with 43% against A(H3N2) and 73% against influenza B 4
Age-Specific Effectiveness Patterns
Vaccine effectiveness varies substantially by age group, with healthy adults under 65 achieving 70-90% protection when strains are well-matched, while elderly persons show lower antibody responses but still gain critical protection against severe outcomes. 5
Among elderly persons living outside nursing homes: 30-70% effective in preventing hospitalization for pneumonia and influenza 5
Among nursing home residents: 30-40% effective against influenza illness, but 50-60% effective in preventing hospitalization/pneumonia and 80% effective in preventing death 5
Among healthy adults <65 years: 70-90% effective when vaccine and circulating viruses are well-matched 5
Critical Clinical Implications
Even when vaccine effectiveness against mild illness is suboptimal, vaccination still provides substantial protection against severe outcomes including hospitalization, ICU admission, and death. 1
Why You Should Still Vaccinate
The CDC recommends continuing vaccination throughout the influenza season regardless of interim effectiveness estimates because: 1
- Vaccine can prevent serious outcomes even when effectiveness against mild illness is reduced
- Vaccine may protect against other influenza viruses that could circulate later in the season
- Influenza activity can persist through February, March, or later 6
Common Pitfalls to Avoid
Do not wait for "perfect" timing or effectiveness data before vaccinating - influenza season timing is unpredictable and vaccine effectiveness wanes over time (approximately 7-11% per month) 6
Do not assume poor effectiveness against one strain means no benefit - the vaccine is quadrivalent and protects against multiple strains 1
Do not delay vaccination in patients with minor illnesses without fever - this leads to missed opportunities for protection 6
How to Find Current Season Data
To determine effectiveness for the actual current influenza season, you need to:
- Check CDC's weekly FluView reports for interim VE estimates (typically released mid-season)
- Review the antigenic characterization data showing match between vaccine and circulating strains
- Monitor which influenza subtypes are predominantly circulating
The bottom line: Annual influenza vaccination remains recommended for all persons ≥6 months as the best strategy for preventing influenza and its complications, even in seasons with suboptimal effectiveness against mild illness. 2, 4