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Healthcare Worker Influenza Immunization

Authors: Pritish K. Tosh, MD; Gregory A. Poland, MDFaculty and Disclosures



Immunization of healthcare workers (HCWs) against influenza is a patient safety and quality-of-care issue. Annual vaccination of HCWs against influenza has been recommended by the US Centers for Disease Control and Prevention (CDC) since 1981.[1] Priority vaccination of this population is strongly encouraged to protect both the HCWs and the patients who they serve.[1] HCWs are frequently exposed to influenza; even when they are asymptomatic, they can transmit the virus to those around them, especially the elderly and immunocompromised.[2] Influenza vaccination of HCWs not only reduces the disease burden in those vaccinated, but also has been shown to reduce the rate of influenza disease and overall mortality in the patients under their care.[1,3] Despite local and national efforts to encourage influenza vaccination, the overall vaccination rate among HCWs in the United States remains unacceptably low at approximately 40%.[4]

Hospital-Acquired Influenza

Influenza is the leading infectious disease killer in the United States; 36,000 deaths and more than 200,000 hospitalizations are attributed to it each year.[1,5] Specific populations most at risk for serious complications from infection (infants, the elderly, and the immunocompromised) are recommended to receive annual influenza vaccination.[1] These populations are also frequently in contact with HCWs, and nosocomially acquired influenza infection is relatively common in settings of low HCW vaccination. These infections are especially devastating in transplant units, pediatric wards, and intensive care units.[6-8]

Unvaccinated HCWs have been repeatedly implicated in hospital outbreaks of influenza. A 1998 outbreak in a neonatal intensive care unit infected 19 of 54 patients, one of whom died; only 15% of the HCWs working in the unit had received influenza vaccination that year.[9] Another especially devastating hospital-wide influenza outbreak occurred in a bone marrow transplant unit. Of the 25 patients found to have hospital-acquired influenza infection, 40% were from the bone marrow transplant unit; 2 of these patients died.[10] Just as in the previous example, only 12% of the HCWs in the bone marrow transplant unit were vaccinated against influenza.[10] An influenza outbreak in a Spanish hospital occurred during a time when influenza was not circulating in the community.[11] Of the 57 HCWs and 23 patients exposed, 31% and 13% developed culture-confirmed influenza disease, respectively. In this situation, only 7% of HCWs had received influenza vacation. One patient who had AIDS and was undergoing chemotherapy for lymphoma died from the infection.[11]

Although these published outbreaks serve as examples highlighting the scope of the problem, nosocomial influenza transmission remains underrecognized. The extent of the problem becomes evident when aggressive surveillance mechanisms are used, revealing that hospital-acquired influenza can account for up to one third of all influenza cases when HCW vaccination rates are low.[12,13]

Unvaccinated HCWs contribute to nosocomial influenza transmission both by asymptomatic shedding of the virus and by coming to work while ill. Influenza infection is asymptomatic in approximately half of all healthy adults; however, asymptomatic HCWs still shed the virus for several days.[2] Unvaccinated HCWs can thus jeopardize their patients even though they do not themselves feel ill. Unfortunately, those who do develop symptoms related to their influenza infection frequently come to work while ill, further jeopardizing their patients and coworkers.[14-16] During the neonatal intensive care unit influenza outbreak described earlier, only 29% of the HCWs who were symptomatic from influenza infection took time off from work.[9] Therefore, because HCWs can transmit influenza to their patients whether they are symptomatic, primary prevention with influenza vaccination is critical.

Influenza Vaccines

Two types of influenza vaccine are currently available in the United States for annual influenza vaccination: intramuscularly administered trivalent inactivated influenza vaccine (TIV) and intranasally administered live attenuated influenza vaccine (LAIV). TIV is created by formalin inactivation and purification of hemagglutinin and neuraminidase surface antigens of the 3 circulating influenza strains.[1] LAIV is created by mating the circulating influenza strains with a cold-adapted strain, resulting in a live virus expressing the hemagglutinin and neuraminidase of the circulating strains but retaining the attenuation and cold adaptation of the donor strain.[1] Both of these vaccines are recommended for use in HCWs; however, TIV should be preferentially given to those caring for highly immunocompromised patients in reverse isolation due to the theoretical risk for transmission of the live virus.[1] These vaccines have been shown to be similarly effective in healthy adults, with effectiveness rates of 70% to 90% when the vaccine strains are well matched to the circulating strains.[1,14,17,18] Both vaccines are well tolerated, with TIV being associated with injection site soreness more commonly than placebo and LAIV being associated with mild, transient rhinorrhea and low-grade fever more commonly than placebo.[1,14,15,17,19,20]

Many HCWs forgo influenza vaccination due to the misperception that influenza vaccines cause influenza illness and are ineffective.[6,16, 21-28] This likely stems from the wide prevalence of other respiratory viruses during the season that the vaccine is given. Studies with TIV have repeatedly confirmed that the rate of noninfluenza respiratory illness following influenza vaccination is identical to that following placebo.[1,14,15,17,29] Studies with LAIV have shown the associated rhinorrhea and low-grade fever to be mild and transient and thus unlikely to be identified as symptoms of influenza.[19,20] Furthermore, the misconception that the vaccine is ineffective is also likely perpetuated by the presence of other wintertime viruses; indeed, even HCWs with poor influenza vaccination rates are 3 times more likely to develop rhinovirus infection than influenza infection.[30]

The benefits of influenza vaccination have been repeatedly demonstrated. Influenza vaccination of working adults reduces upper respiratory infections by 25%, physician visits by 44%, and sick days off work by 43%.[17] The effect on the patients under the care of vaccinated HCWs is even more profound. A Scottish study randomized long-term care centers either to offer influenza vaccination to their HCWs or not. The care facilities at which HCWs were offered influenza vaccination demonstrated a 40% reduction in all-cause mortality among patients compared with care facilities that did not offer the vaccination to their HCWs.[3] The mortality reduction benefit of influenza vaccination may have even been underappreciated because the vaccination rate in the facilities that offered influenza vaccination was only 51% (compared with 5% in the other facilities).

A study at the University of Virginia Health System confirmed the effectiveness of influenza vaccination among HCWs with regard to their health as well as the health of their patients.[12] The 600-bed hospital had an influenza vaccination compliance rate of 4% during the 1987-1988 influenza season, which increased to 67% by the 1999-2000 season. Corresponding with this increase in influenza vaccine acceptance was a reduction in the proportion of influenza cases involving HCWs from 42% of all influenza cases during 1990-1993 to 9% during 1997-2000. Furthermore, the proportion of nosocomial influenza cases decreased from 32% during the 1987-1988 season to 3% during the 1998-1999 season.[12] Other institutions have seen similar reductions in nosocomial influenza cases with increased HCW vaccination.[31]

Cost Savings

Although reductions in HCW illness and patient mortality are the most important benefits of HCW influenza vaccination, there is an added benefit of cost savings. Each year, unvaccinated HCWs miss an average of 1.30 workdays due to influenza, costing $137 in work loss.[32] After considering the costs of vaccination, a study by Nichol and associates[17] found that influenza vaccination of healthy working adults saved an average of $47 per person annually due to the reduction in doctor visits and sick days. Recently, Medicare announced that hospital-acquired infections -- including nosocomial influenza -- will no longer be reimbursed.[33] Because nosocomial influenza can represent up to 30% of influenza cases in areas of low HCW vaccination, the financial burden to institutions with low HCW vaccination rates will soon become apparent.[31,33,24]

HCW Vaccination Rates

Despite recommendation by the CDC that all HCWs receive annual influenza vaccination, the influenza vaccination rate in the United States remains unacceptably low at approximately 40%.[1,4,22] Nurses, nurse aides, and technicians are the subgroups of HCWs with the lowest influenza vaccination rates.[21,26,27]

A survey of HCWs from several different healthcare settings in North Carolina was conducted to determine the institutional and individual barriers related to low influenza vaccination compliance.[6] Approximately 38% of the respondents worked at healthcare facilities with written policies on employee influenza vaccination, and only 2% worked at facilities where influenza vaccination was mandatory (mostly in the home health setting). On the level of the individual HCW, 7% of respondents reported the cost of the vaccine as a barrier to vaccination, highlighting the need for healthcare facilities to assume the cost of vaccination. The survey also emphasized the need for institutional educational efforts because 68% of respondents cited "fear of side effects" and 53% cited "perceived ineffectiveness of the flu vaccine" as barriers to vaccination.[6] These and other findings of widely held misconceptions with regard to influenza vaccination among HCWs are prevalent, as demonstrated by numerous other studies.[16, 21-28]

Mandatory HCW Influenza Vaccination

Although efforts to improve influenza immunization have been modestly successful in increasing HCW vaccination, vaccination rates rarely exceed 70% even after aggressive programs are instituted. This has led to the proposition that influenza vaccination be made mandatory for HCWs.[37,38] An influenza vaccine mandate, while allowing for informed declination, has been supported by the following health organizations: Infectious Diseases Society of America, Society of Hospital Epidemiologists of America, Expert Panel on Strengthening Adult Immunization, Association of Perioperative Registered Nurses, Association of Professionals in Infection Control, ACIP, Minnesota Department of Health, American Society of Health System Pharmacists, American Academy of Pediatrics, Healthcare Infection Control Practices Advisory Committee, US Public Health Service, American Medical Association, and American College of Physicians, among others.[39] Additionally, several states have enacted legislation requiring influenza vaccination for HCWs in long-term care facilities.[22]

Previous HCW mandates -- including rubella vaccination, hepatitis B vaccination, and annual screening for tuberculosis -- have resulted in nearly universal compliance with the recommendation and are generally accepted by HCWs.[37,38] After instituting a mandatory influenza vaccination policy for HCWs, institutions, such as the Virginia Mason Clinic, have seen compliance rates exceeding 98%.[40] After decades of effort to increase voluntary influenza immunization among HCWs, a universal mandate appears to be needed to protect patients from a completely preventable infection.


Influenza is a deadly disease, especially for infants, the elderly, and the immunocompromised. Unvaccinated HCWs are known to be vectors of this disease and have been implicated in outbreaks. Furthermore, influenza vaccines are extremely safe and highly effective. The current level of vaccination is unacceptably low, and patients remain at risk for nosocomial influenza as long as HCWs remain unvaccinated. Institutional programs incorporating education as well as convenient vaccine administration are needed to improve HCW vaccination rates. However, voluntary efforts may not be enough. Therefore, mandatory influenza vaccination may be required to ensure that HCWs receive vaccination and that the interests of patients are being met.

Supported by an independent educational grant from GlaxoSmithKline

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