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New data suggest immunization cuts absenteeism
Doctors and nurses who receive influenza vaccine every year may have fewer days of work absence and febrile respiratory illness during flu season, according to a new study that supports employee health policies of annual influenza vaccination for health care workers.
The prospective trial found that not only was influenza vaccine effective in preventing infection in HCWs; it also decreased cumulative days of reported febrile illness by 12 days per 100 subjects and reduced days absent by 10 days per 100.1
Study data also show that unvaccinated HCWs have a 14% risk of developing influenza type A or B infection, and that infection increases the risk of febrile respiratory illness or work absence fourfold.
Influenza infection among study subjects was associated with an additional 1.5 days of febrile respiratory illness and 0.5 days of work absence during an influenza season. The researchers maintain that their data provide a point estimate of "an absolute vaccine effect of 11 work absence days that were averted per 100 vaccinees and confirm the relative effect of 88% reduction in infection."
Study participants were 264 healthy physicians, nurses, and respiratory therapists from two large teaching hospitals in Baltimore. They were studied over three consecutive influenza seasons between 1992 and 1995. Mean age was 28.4 years; 57% were women. Vaccines and placebo were administered intramuscularly in October and November 1992, 1993, and 1994. Controls were administered meningococcal vaccine, pneumococcal vaccine, or placebo.
Each week during flu seasons, a study nurse called each participant to inquire about illnesses during the previous week, and recorded specific symptoms of respiratory illness and work absences due to illness. Blood specimens were obtained to check for influenza infection.
Infection rates for flu vaccine recipients and among controls were not altered by their vaccine experience in the previous year. Controls who received vaccine the previous year were infected at the same rate as controls not vaccinated the year before. The researchers found no evidence of "vaccine carryover," further supporting their recommendation for annual HCW vaccination.
The study apparently is the first assessment of the effect of influenza vaccine on health care professionals in a randomized, double-blind, controlled trial over three successive flu seasons. While a previous study of healthy adults showed vaccination resulted in a 0.5-day absenteeism reduction during a severe influenza attack season,2 other studies specific to HCWs’ absenteeism and infection rates have produced mixed results, the Baltimore researchers point out.
Convincing HCWs to comply with annual influenza vaccination programs is an ongoing struggle for most hospital occupational health professionals. U.S. Centers for Disease Control and Prevention guidelines list influenza as a disease for which immunization is strongly urged and call for health care facilities to offer vaccines before influenza season to all workers who have contact with high-risk patients.3 Nevertheless, an unpublished 1993 CDC survey found that only 17% of hospitals contacted were vaccinating 50% or more of targeted employees.
"This population has shown it is not willing to get vaccinated at very high rates," says James A. Wilde, MD, lead researcher in the Baltimore study, former fellow in pediatric emergency medicine for the first two years of the study at Johns Hopkins University, and former faculty member at Case Western Reserve University, Cleveland, in the emergency medicine and infectious disease divisions during the study’s third year.
One reason for vaccine avoidance is the low influenza attack rate, Wilde says.
"The problem is that even in a severe influenza season, the attack rate is about 20% [of unvaccinated people]. In a mild season, maybe only 2% to 5% get flu," he says. "That’s the argument that some people give: The risk is not that high, so why should I get a shot every year for an infection that I may get only once in five or 10 years?"
HCWs also worry about vaccine side effects, especially getting influenza itself, "which is not possible," he points out, and about Guillain-Barre syndrome, which resulted from the "swine flu" vaccine in 1976.
"That fear has persisted for the past 25 years, despite the fact that no vaccine since then has been associated with Guillain-Barre syndrome," he says. "There is a lot of misinformation, even among physicians."
HCWs often reject vaccination if they were vaccinated the year before and still became ill, Wilde adds, but he explains that many non-flu viruses circulate during influenza season.
"People associate any febrile respiratory illness during influenza season with influenza, but it’s not the same thing," he says. "Lots of other viruses can give you fever and respiratory symptoms, although the severity of illness from those viruses is not as high as influenza. Because [HCWs] have had that experience, they say they won’t bother to get the flu vaccine because [they think] it doesn’t work."
However, the main reason HCWs don’t get vaccinated is that "it doesn’t seem important to them," says Wilde, who now is with the department of emergency medicine at the Medical College of Georgia in Augusta. "They don’t worry about it because they figure it’s no big deal if they’re sick for a few days."
This attitude ignores the crucial patient protection factor, he points out. Influenza may be nothing more than a three- or four-day "nuisance" for a healthy adult, "but if you take it with you to the hospital and infect a cancer or renal dialysis patient, those people can die from the infection."
Wilde suggests that education efforts directed at HCWs include the results of a 1997 study in long-term care hospitals. It showed that when more than 60% of staff were vaccinated, total patient mortality related to influenza was reduced significantly, while high patient vaccination rates were not associated with significant effects on mortality.4
Wilde’s study revealed important findings related to potential influenza transmission from HCWs to patients.
First, study participants were likely to report to work even when experiencing a febrile respiratory illness, a practice that increases the potential for infecting patients. Wilde notes, however, that 75% of study subjects were resident physicians, and that possibly not all HCW groups would be as reluctant to miss time from work.
Second, even if each unvaccinated employee has only a 20% chance of getting flu in a given year, in a medical center with 1,000 employees, 200 employees could contract influenza. That number is significant.
"If those 200 people do get influenza and come to work, they’re going to spread it to a vulnerable population," he notes. "We found that the people who showed evidence for having influenza based on serology had a much lower number of days of absenteeism than they did days with fever and illness. So these people were coming to work with fevers, and that means presumably they were spreading influenza to people they were working with and to their patients."
Cumulative days of reported febrile respiratory illness were 41 per 100 subjects in the control group and 29 per 100 subjects in the group receiving flu vaccine. Days of absence were reduced from 21 per 100 subjects in controls to 10 per 100 subjects in flu vaccinees. While that number represents only 1/10 of a day per employee, there potentially are 100 days less absence if 1,000 employees are vaccinated.
"Looking at it from the administrator’s standpoint, 100 days of prevented absence in an influenza season is a pretty good chunk of days" and helps justify more aggressive influenza vaccination programs for employees, Wilde states.
Efforts to increase flu vaccination compliance in HCW populations have been "less than major," he adds. While many hospitals make vaccine available, merely sending employees e-mail memos to "come and get it" is inadequate, garnering "10% to 50% compliance at best."
More concerted efforts to increase compliance include taking influenza vaccine carts to employees on their wards, Wilde says, a suggestion also offered by officials of the CDC’s national immunization program. (See Hospital Employee Health, November 1998, pp. 137-139.) Obtaining vaccine free of charge is an incentive for employees, as well. (See related story, p. 68.)
"Our study gives administrators more reason to do more aggressive marketing of the influenza vaccine to their employees," he says.
1. Wilde JA, McMillan JA, Serwint J, et al. Effectiveness of influenza vaccine in health care professionals: A randomized trial. JAMA 1999; 281:908-913.
2. Nichol KL, Lind A, Margolis KL, et al. The effectiveness of vaccination against influenza in healthy, working adults. N Engl J Med 1995; 333:889-893.
3. Centers for Disease Control and Prevention. Immunization of health care workers: Recommendations of the Advisory Committee on Immunization Practices (ACIP) and the Hospital Infection Control Practices Advisory Committee (HICPAC). MMWR 1997; 46(RR-18):1-42.
4. Potter J, Stott DJ, Roberts MA, et al. Influenza vaccination of health care workers in long-term care hospitals reduces the mortality of elderly patients. J Infect Dis 1997; 175:1-6.