Effects of Influenza Vaccination in the United States During the 2018-2019 Influenza Season.
Level 4 - case-series / case-control
Mathematical modeling study based on observational surveillance and test-negative case-control effectiveness data
PubMed 31905401 · doi:10.1093/cid/ciz1244
What was done
Researchers used a mathematical model and a Monte Carlo algorithm to estimate the numbers and 95% uncertainty intervals (UIs) of influenza-associated illnesses, medical visits, hospitalizations, and deaths prevented by vaccination in the United States during the 2018-2019 season. The model synthesized national age-specific vaccine coverage data, virus-specific vaccine effectiveness estimates from the US Influenza Vaccine Effectiveness Network, and population-based hospitalization rates from the Influenza Hospitalization Surveillance Network.
What was found
Influenza vaccination prevented an estimated 4.4 million (95% UI, 3.4 million-7.1 million) illnesses, 2.3 million (95% UI, 1.8 million-3.8 million) medical visits, 58,000 (95% UI, 30,000-156,000) hospitalizations, and 3,500 (95% UI, 1,000-13,000) deaths during the 2018-2019 season. Vaccination prevented 14% of projected hospitalizations associated with A(H1N1)pdm09 overall and 43% among children aged 6 months-4 years.
Why it matters
This study demonstrates that influenza vaccination averts substantial morbidity, mortality, and healthcare utilization even in seasons where circulating A(H3N2) strains are largely mismatched to the vaccine, driven by effectiveness against well-matched A(H1N1)pdm09 strains.
Limits
The findings are based on mathematical modeling and simulated estimates rather than directly observed counts. The abstract reports wide uncertainty intervals for severe outcomes such as deaths (1,000 to 13,000) and hospitalizations (30,000 to 156,000), reflecting dependence on the underlying precision of surveillance and vaccine effectiveness estimates.
Cited by
- supports The prior year's influenza vaccine was approximately 30% effective.