Put down the smartphone and the tablet and forget those reminder calls and postcards for flu vaccines. A sizable study of four primary care clinics serving low income communities in New York found that text messaging can really move the needle.

Findings from a  study involving 9,213 children and adolescents, presented in the April 25 edition of the Journal of the American Medical Association, reported a four-point bump in a group reached with multiple text messages (43.6% brought their children in for a vaccination) versus those who got one phone call (39.9%). Extrapolated to the entire US population, that’s another 2.5 million kids.

“This study highlights the potential for patient reminder/recall but also its challenges,” wrote the authors. “The potential is substantial, and in the right setting with automated, integrated information systems, text message reminders can target large numbers of patients at relatively low cost. ”

Traditionally, the researchers said, patient reminder/recall methods have consisted of letters or postcards or telephone calls made by office staff with autodialer machines capable of calling hundreds of families per hour, but many patients fall through the cracks because of changing or inaccurate patient telephone and address info.

Other factors in play include patients’ willingness to immunize their children, understanding of the disease and the vaccine, ease of making an appointment and access to transportation.