Analysis of large-scale national data indicated laws that encourage vaccination of hospital staff against influenza substantially reduced viral spread and protected the most vulnerable populations. These findings were published in the Annals of Internal Medicine.
State-level longitudinal data from 1995 to 2017 comprising state influenza vaccination laws, pneumonia mortality rates, and influenza mortality rates from 14 states were assessed for patterns of successful and unsuccessful legislative policies.
In 1995, less than 2% of hospital workers were affected by influenza vaccination laws. At the conclusion of this study period, 38% of hospital workers were subject to vaccination law. Vaccination rates increased from 43% of hospital workers during the 1997 to 1998 influenza season to 87% during the 2016 to 2017 season.
The investigators observed that states with increased mortality rates from influenza tended to adopt vaccination laws as a reaction. In years when influenza mortality was low (1995-1996; 2001-2002), no state enacted changes to the law, but in those years when influenza mortality was high (2007-2008; 2016-2017), 12 states adopted vaccination laws.
States that changed vaccination laws had larger decreases in mortality rates than states that did not enact a law (mean, -0.16 deaths per 100,000 persons per month; 95% CI, -0.29 to -0.02; P =.022). For the 2016 to 2017 influenza season, 1822 deaths (95% CI, 275-3337) were avoided after implementing vaccination laws for hospital workers.
The reduced mortality rate was primarily observed among people 65 years or older (mean, -1.19 per 100,000 older persons per month; 95% CI, -2.09 to -0.26; P =.013) rather than people younger than 65 (mean, -0.01 per 100,000 persons per month; 95% CI, -0.03 to 0.02; P =.66).
After enacting vaccination laws, the decrease in influenza mortality continued to grow. At 1 year after adoption of the law, the change in monthly influenza deaths was -0.17 per 100,000 persons (95% CI, -0.32 to -0.01; P =.041). At 2 years, it was -0.20 (95% CI, -0.38 to -0.02; P =.029), and at 3 years, it was -0.34 (95% CI, -0.54 to -0.13; P =.002).
This study was limited by not analyzing hospital-acquired influenza infections; however, those data were not available.
The study authors concluded that laws promoting vaccination among hospital workers successfully prevented influenza-related deaths among vulnerable populations.
Carrera M, Lawler EC, White C. Population mortality and laws encouraging influenza vaccination for hospital workers. Ann Intern Med. Published online January 5, 2021. doi:10.7326/M20-0413