The original national sample consisted of 1,606 U.S. physicians. Survey responses returned by November 27, 2000, were included in the analysis (n = 969; response rate, 60%). Response rates differed slightly between family physicians and internists (62% vs 59%), and between geriatricians and generalists (64% vs 60%), but these differences were not statistically significant. Respondents were more likely than nonrespondents to be board certified in their specialties (81% vs 73%; P < .001), but did not differ from nonrespondents with respect to year of graduation from medical school.
Characteristics of Physicians Administering Influenza Vaccine
Among respondents, 17 were ineligible because of retirement or other lack of current clinical activity. Of the remaining 952 physicians, 756 (79%) reported that they typically administer influenza vaccine in their practices. Family physicians are significantly more likely than internists to administer influenza vaccine (82% vs 76%; P < .05).
Practice characteristics of the 756 respondents who typically administer influenza vaccine appear in . Most physicians were board certified in their self-identified field, one third had graduated from medical school more than 20 years ago, and more than half worked in private, independent practice; these proportions did not differ significantly between internists and family physicians. Geriatricians were significantly more likely than generalists to work in university-based (14% vs 3%; P < .001) or hospital-affiliated practices (23% vs 15%; P < .05), and were significantly less likely to work in private, independent practice (44% vs 62%; P < .001).
Characteristics of Physicians Who Typically Administer Influenza Vaccine
Respondents in private, independent practice were significantly more likely than physicians in other settings to have graduated from medical school more than 20 years ago (37% vs 27%; P < .005); overall, they constituted two thirds of all physicians who graduated more than two decades ago. Providers in private, independent sites were also significantly less likely to be board certified than physicians working in other practice settings (78% vs 87%; P < .005).
Typical Influenza Vaccine Administration Practices
Physicians reported providing the vast majority of influenza vaccine doses to individuals at high risk for complications of influenza—those with chronic illnesses and those 65 years of age or older. Only 7% of physicians said that they provided over half their doses to healthy patients not at increased risk. The proportion of high-risk patients to whom respondents administer influenza vaccine did not differ significantly by physician specialty or subspecialty, practice setting, years since medical school graduation, or board certification status.
Respondents most often initiate annual influenza vaccination in September (21%) and October (75%), and most physicians typically finish administering influenza vaccine in December (31%), January (30%), or February (20%). The typical duration of vaccine administration ranges from 1 to 8 months, with 80% of respondents administering vaccine for 3 to 5 months. Respondents did not differ significantly by specialty or subspecialty in their duration of vaccine administration.
Based on CDC influenza surveillance data since 1982, the typical peak of influenza activity occurs in the fourth week of January. Comparing historical national influenza activity with physicians' reported vaccine administration periods, 43% of respondents stop vaccinating before January 1, i.e., before the typical national peak. Only 27% of respondents indicated that they typically continue influenza vaccination past the typical peak, into February and later. Family physicians were significantly more likely than internists to continue vaccinating past the typical national peak (31% vs 21%; P < .005), as were physicians practicing in a public clinic compared to respondents in other clinical settings (40% vs 27%; P < .005).
Capacity to Contact High-risk Patients
Physicians varied in their practices' capacity and experience in identifying and contacting patients at high risk for complications of influenza. Over 90% of physicians reported that they relied—in whole or in part—on office visits to target high-risk patients. Half of physicians thought their practices were able to generate lists of patients with specific chronic illnesses, and 75% thought their practices were able to generate lists of patients aged 65 and older. However, only 26% of physicians had used mail or telephone reminders in the past to contact high-risk patients regarding influenza vaccination. Internists were slightly more likely than family physicians to have had experience with reminder systems (28% vs 24%), and geriatricians were somewhat more likely than generalists to have used reminders (32% vs 25%), but these differences were not statistically significant.
Physicians who described their practice settings as a physician network (e.g., staff-model managed care organizations or multi-site group practices) are significantly more likely to have used reminders than physicians who work primarily in private independent practices, university- or hospital-affiliated settings, or public clinics (41% vs 24%; P < .005). Use of reminders did not differ significantly by board certification status or years since graduation from medical school.
We used multivariable logistic regression models to compare the effect sizes of variables associated with use of reminder systems (). Controlling for subspecialty, board certification, and years since graduation from medical school, physicians practicing in a physician network were twice as likely to use reminders as physicians in other clinical settings. In the same model, geriatricians appeared more likely than generalists to use reminder systems, but this trend was not statistically significant.
Multivariable Logistic Regression Models of Use of Reminder Systems
In a model regarding practice characteristics specific to influenza vaccine (), use of reminders was significantly more common among physicians whose practices could generate lists of chronically ill patients or elderly patients, when controlling for duration of vaccination period, proportion of doses for chronically ill patients, and continuation of vaccine administration beyond the typical national peak. Respondents who typically continue vaccinating past the national peak of influenza activity appeared more likely to use reminders than those who stop vaccinating at or before the peak, but this association was not statistically significant.
Reluctance to Administer Influenza Vaccine during the Influenza Season
Physicians were asked whether they would be hesitant to administer influenza vaccine after local influenza activity had begun. Nearly half (43%) of physicians reported they were hesitant or neutral (“hesitant providers”) about administering vaccine in this circumstance.
As expected, providers hesitant to administer vaccine after the onset of local influenza disease activity were significantly more likely to report that they typically end vaccine administration prior to the national peak of influenza activity (53% vs 35%; P = .001). Hesitant providers were also significantly more likely to report shorter typical vaccine administration periods: they comprised 51% of all physicians with durations of 3 months or less, but only 38% of physicians who usually administer vaccine for 4 months or longer (P < .001).
The proportion of hesitant providers was not significantly different across specialty or subspecialty groups, and did not differ by year of medical school graduation or by use of reminder systems. However, physicians who are not board certified were significantly more likely to be hesitant than board-certified providers (57% vs 40%; P < .001). In addition, physicians who typically administer 20% or more of their vaccine doses to standard-risk individuals were significantly more likely to be hesitant than physicians who provide the bulk of their doses to high-risk patients (47% vs 40%; P < .05).