The Johns Hopkins Gazette: March 22, 1999
Mar. 22, 1999
VOL. 28, NO. 27


Study Shows Flu Shots Keep Health Workers On the Job

By Kathy Moore
School of Public Health
Johns Hopkins Gazette Online Edition

Flu shots, generally accepted as necessary for the elderly and for other adults and children at high risk for complications, may also have tremendous benefits for health care workers. A new study has shown that doctors and nurses lose fewer days from work because of the flu when they are vaccinated annually. The study authors also postulated that health workers likely spread less disease when they get influenza vaccine and stay healthy.

In a randomized, double-blind, controlled study to determine the effects of the flu vaccine on health care workers' illness and work absence--the first to be carried out over three successive epidemic seasons--researchers at the schools of Public Health and Medicine cleared up contradictory findings about whether flu shots really made a difference in keeping health care workers on the job. Their study appears in the March 10 issue of the Journal of the American Medical Association.

Senior author Mark C. Steinhoff, professor, International Health, said, "Although the flu vaccine has been demonstrated to be effective in reducing sickness and death in young adults and the elderly, there have been contradictory findings as to whether the vaccine decreases the rate of influenza or sick leave among health care professionals."

Although the U.S. Advisory Committee on Immunization Practices has recommended since 1981 that health care professionals get the flu vaccine, rates of influenza vaccination among health care professionals are consistently low, between 16 percent and 51 percent. Some critics of annual flu shots cite "vaccine carryover"--when a previous year's vaccination decreases the protection gotten from the vaccine in subsequent years--but the authors found no evidence of carryover and recommended that hospitals institute annual influenza vaccinations for health care professionals. Two hundred sixty-four hospital-based health care professionals were randomly assigned to receive either an influenza vaccine or a control injection (either meningococcal vaccine, pneumococcal vaccine or placebo over a three-year period). The mean age was 28.4 years; 77 percent were resident physicians, 57 percent were women, and 18 percent were nurses.

All vaccines and placebos were administered in October and November of 1992, 1993 and 1994. Each week during the flu season, a study nurse called all participants on the telephone, inquired about illnesses during the previous week and recorded specific symptoms of respiratory illness and absences from work due to illness. Blood specimens were obtained to check for influenza infection.

The overall incidence of influenza infection was 1.7 percent among vaccine recipients compared to 13.4 percent among controls. The rate of influenza type A infection per 100 study subjects was 1.1 in influenza vaccinees and 8.9 in controls, for an effectiveness of 88 percent. The rate of influenza type B infections was 0.6 in influenza vaccinees and 5.0 in controls, for an effectiveness of 89 percent. Individuals who remained unvaccinated had a 14 percent risk of developing influenza type A or B infection. Influenza infection was associated with workers having an additional 1.5 days of febrile respiratory illness and missing 0.5 more days of work.

Subjects who had received the influenza vaccine reported a total of 28.7 days of respiratory illness with fever per 100 subjects, compared with 40.6 days per 100 controls. Vaccinated subjects missed 9.9 days of work per 100 subjects versus 21.1 days per 100 controls. The health care professionals actually reported more total days of respiratory illness and fever than days absent from work, suggesting they sometimes report for duty even with fever and respiratory illness, a practice that risks spreading flu to debilitated or elderly hospital patients.

The influenza infection rates of flu-vaccine recipients and of controls not getting the flu shot were not altered by a person's vaccine experience in the previous year. Thus, control subjects who had received the vaccine during the previous season were infected at the same rate (15 percent) as controls who had not been vaccinated during the prior year. Steinhoff and his colleagues conclude that their new data confirm the benefits of annual vaccination for health care workers.