Thanks to changes in state laws, pharmacists are playing an increasingly critical role in increasing influenza-immunization rates across the United States.

That’s according to a study in Clinical Therapeutics, which analyzed how immunization rates were affected by policy changes allowing pharmacists to provide flu vaccinations. The review was conducted by Avalere Health in Washington, DC, and the National Association of Chain Drug Stores in Arlington, Virginia.

For the study, researchers compared influenza-immunization rates across states before and after policy changes permitting pharmacists to administer them. Survey data from the Behavioral Risk Factor Surveillance System on influenza-immunization rates between 2003 and 2013 was used for the analysis.

All 50 states and the District of Columbia now allow pharmacists to administer immunizations to adults, with those changes in some states occurring in the 1990s, while others passed the regulations more recently. Michigan began the trend in 1990, and half of states changed their policies in 2004 and later, with two states—South Carolina and Louisiana—not changing rules on allowing pharmacists to provide vaccines until 2010, according to background information in the study.

Results of the analysis show that as states altered policy to allow pharmacists to administer influenza immunizations, the odds that an adult resident received an influenza immunization increased, and the effect increased over time. During the study years, the average percentage of Americans receiving seasonal influenza immunizations was 35.1%, increasing from 32.2% in 2003 to 40.3% in 2013. (The increase wasn’t consistent; the rate dropped as low as 25.5% in 2005, possibly related to an influenza vaccine shortage from 2004 to 2005.)

The leap in influenza-immunization levels was 2.2% to 7.6% in adults aged 25 to 59 years, with the largest bump for those aged 35 to 39 years, but without significant change for those younger or older. The percentage of American adults immunized against the flu increased with age, ranging from 21.8% for those aged 18 to 24 years to 71.3% for those aged 75 years and older. Immunization rates also rose with education—from 30.8% for those with no high school diploma to 39.7% for those with 4 or more years of college—and with income—from 32.1% for income less than $15,000 to 37.7% for income above $75,000.

“The present study suggests that regulations implemented to expand pharmacists’ role in health care delivery through the administration of seasonal influenza immunizations have had a positive impact on the national efforts to increase immunization rates,” study authors point out. “Our findings show that states had significantly higher long-run seasonal influenza immunization rates among most nonelderly adults after policy changes allowed pharmacists to administer immunizations.”

The primary reason, according to the researchers, is that “pharmacies and other nontraditional settings may offer accessible venues for patients when implementing other public health initiatives.”