Brief Report

Does vaccinating ED health care workers against influenza reduce sickness absenteeism?

Stewart Siu-Wa Chan MBBS*

Emergency Department, Prince of Wales Hospital, Hong Kong

Received 6 November 2006; revised 17 January 2007; accepted 3 February 2007

Abstract

This study aims to investigate the association between influenza vaccination of health care workers (HCWs) and sickness absenteeism. A retrospective cohort study was conducted in an emergency department (ED) of an acute care hospital. All full-time HCWs except physicians (73 nurses and health care attendants) were included. Influenza vaccine was administered to HCWs on a voluntary basis commencing November 2004. Absenteeism due to influenza-like illness during the period from January to October 2005 was noted.

The mean number of cumulative sick leave days per person was smaller (1.0 days against 1.75 days) in vaccine recipients than in vaccine nonrecipients although the difference was not statistically significant. A significantly larger proportion of subjects took sick leave because of influenza-like illness in the vaccine nonrecipient group (55% against 30.3%, P = .034).

Conclusion: Influenza vaccination of HCWs in the ED setting is significantly associated with a fewer number of HCWs requiring sick leave.

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Introduction

Influenza vaccination for health care workers (HCWs) has been widely recommended by health authorities [1-3]. Since 1993, the Centers for Disease Control and Prevention (CDC) has recommended annual influenza vaccination for all HCWs [1,2]. The CDC Healthcare Infection control Advisory Committee and the Advisory Committee on Immunization Practices recommend the provision of influenza vaccination to HCWs at the work site, free of charge, as part of employee health programs [1]. However, the rate of vaccination uptake

* Accident and Emergency Medicine Academic Unit, Prince of Wales Hospital, Shatin, NT, Hong Kong. Tel.: +852 2632 2219; fax: +852 2337

3226.

E-mail address: [email protected].

by HCWs is not high. According to a recent analysis of data from the 2000 National Health Interview Survey in which 1651 HCWs were included within 12 months of survey, the vaccination rate in the United States was reported to be only 38% [4]. Furthermore, a recent systematic review of 18 relevant studies also concluded that despite recommenda- tions, less than 25% of HCWs in Europe and the United Kingdom are vaccinated against influenza [5].

Health care workers of emergency departments (ED) have a relatively higher risk of exposure to influenza. Because of implications to infection control and patient safety and the general low vaccination uptake by HCWs, implementation of an effective vaccination program for HCWs can be a challenging task to ED administrators and managers [6]. It is recommended that efforts should be made to educate HCWs regarding the benefits of vaccination [1].

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The benefits of vaccination and protection of staff against Influenza infection include prevention of transmissions to patients and the reduction of economic loss due to staff absenteeism [7]. However, among vaccine nonrecipients, doubts about the efficacy and necessity of influenza vaccination are common, particularly among nurses [8-11]. To increase the vaccination rate, HCWs need to be convinced about the effectiveness of influenza immuniza- tion [12-14]. Reduction in sickness absenteeism at the work site is one important indicator of the effectiveness of vaccination [15].

This is a pilot study to investigate whether and by how much influenza vaccination of HCWs in an ED can reduce influenza-like illness-related absenteeism from work. We postulated that the cumulative number of sick leave days per person, within a given period, is different between influenza vaccinees and vaccine nonrecipients. To help plan and carefully design future studies, we sought to first find out the mean number of cumulative sick leave days per person for influenza vaccinees and for vaccine nonrecipients among the HCWs in our ED setting.

Methods

A retrospective cohort study was conducted in the setting of an ED of a 1200-bed acute care general hospital in Hong Kong, with an ED annual census of 140000 patient visits. All full-time clinical staff members (HCWs) including nurses and health care attendants of the ED from November 2004 to October 2005 were included. Subjects with absence (not sickness related) from the department for longer than 1 month during the previously mentioned study period were

excluded. Physicians were not included in the study.

Data collection

For the 2004-2005 season, influenza vaccine was admin- istered to consenting HCWs commencing November 2004 as part of the hospital’s voluntary staff influenza vaccination program. Influenza vaccinees and vaccine nonrecipients among staff members during the study period were noted from record. As a component of the ED’s infection control program, a reporting system was in place for monitoring staff sick leave patterns to facilitate early identification of any

Table 1 Comparison of age and sex between vaccine
recipients and	vaccine nonrecipients
	Vaccine recipients (n = 33)	Vaccine nonrecipients (n = 40)	P
Mean age in	43.55 (8.85)	40.65 (6.99)	.12
years (SD) Sex-female	75.7 (72.9-78.3)	72.5 (69.7-75.2)	.75
(% [95% CI]) CI indicates confidence interval.

Table 2 Comparison of (a) mean number of cumulative sick

leave days per person and (b) proportion of subjects who took sick leave between vaccine recipients and vaccine nonrecipients

Mean number of

cumulative sick leave days

per person (SD)

Number of subjects who took sick leave

because of influenza-like illness within the

study period (% [95% CI])

Vaccine

recipients (n = 33)

1.0 (2.14)

Vaccine

nonrecipients (n = 40)

1.75 (2.15)

P

.14

30.3

(27.5-33.2)

55.0

(45.2-64.5)

.034

abnormal upsurge of influenza-like illness. The system of data collection was based on the HCW’s self-report of symptoms at the time when sick leave was required, in conjunction with the diagnosis given by the medical practitioner who granted the leave, and subject to the final opinion of the department’s (Nursing) operational manager, who would enter the most likely diagnosis on the data file. Upper respiratory tract infection symptoms, fever, headache, or myalgia were features that would be included in the review as influenza-like illness. An audit of this record was performed together with a study of the record of staff influenza vaccination of the 2004-2005 season. The names of individual staff members were de- identified for the purpose of this study. Absenteeism due to influenza-like illness during the period from January to October 2005 was noted from the departmental record. Absenteeism within 6 weeks of vaccination was not included because of the likelihood that the sickness might be related to the vaccination itself.

For HCWs who were recorded as not having received vaccination, it is theoretically possible that they could have obtained immunization elsewhere, but this is highly unlikely. This is because of the fact that vaccination was provided free of charge and conveniently at the work site and that the vaccination program was thoroughly promoted to all HCWs.

Statistical methods

The differences in (a) the mean number of cumulative sick leave days per person and in (b) the proportion of subjects who took sick leave, from January to October 2005, between the vaccinee group and the vaccine nonrecipient group were analyzed. In addition, the characteristics of subjects who took sick leave for influenza-like illness were compared between the 2 groups. Continuous data were analyzed using t test, and categorical variables were analyzed using v² test. Calculations were performed using the software Programs for Epidemiologists version 4.0 (Sagebrush Press, Salt Lake City, Utah) [16].

Table 3 Characteristics of subjects who took sick leave because of influenza-like illness: comparison between vaccine recipients and vaccine nonrecipients
	Vaccine recipients (n = 10)	Vaccine nonrecipients (n = 22)	P
Mean age in	35.4 (6.95)	37.64 (6.2)	.37
years (SD)
Sex-female	90.0 (59.6-99.5)	63.6 (60.6-66.5)	.12
(% [95% CI])
Mean number of	3.3 (2.79)	3.18 (1.94)	.88
days of cumulative
sick leave days
per person (SD)

As this was a retrospective study, the sample size was known before commencement of the study. There were 33 vaccine recipients and 40 nonrecipients. When comparing the mean number of sick leave days between the 2 groups, for 2-sided a = .05 and b = .20 (power of 80%), a sample size per group of 34 will detect a standardized effect size of 0.7. As recommended by the World Health Organization, the vaccine used for the season studied contained the following: A/New Caledonia/20/99(H1N1)-like virus; A/Fujian/411/ 2002(H3N2)-like virus; B/Shanghai/361/2002-like virus. An inactivated split-virion vaccine (Vaxigrip, Sanofi-aventis, Paris, France) was administered via the intramuscular route.

Results

A total of 73 HCWs (49 nurses and 24 health care attendants) were included. There was no significant differ- ence in age or sex between vaccine recipients (n = 33) and vaccine nonrecipients (n = 40) (Table 1).

The mean number of cumulative sick leave days per person was smaller (1.0 days against 1.75 days) in vaccine recipients than in vaccine nonrecipients although the difference was not statistically significant (Table 2). Nevertheless, a significantly larger proportion of subjects took sick leave because of influenza-like illness during the study period in the vaccine nonrecipient group (55% against 30.3%, P = .034).

Table 3 shows the characteristics of subjects who took sick leave because of influenza-like illness, comparing between vaccine recipients and nonrecipients. There was no significant difference in mean age, sex, and mean number of cumulative sick leave days per person.

Discussion

The CDC recommendation of annual influenza vaccina- tion for all HCWs supports the observation that HCWs are likely to be exposed to many acutely ill patients infected with influenza, are susceptible to influenza infection, and may subsequently transmit this infection to other patients.

Nevertheless, published studies that investigated the bene- fits of influenza vaccination of HCWs are scarce. A Medline search using the terms influenza vaccination and health care workers found only 7 such studies in indexed literature. The outcome measures used in these studies included days absent from work, days of febrile respiratory illness, serologically defined influenza infection, and mortality among patients in the same institution. Evidence from these studies has been conflicting, and only 4 studies investigated the number of days absent from work. None of these studies were conducted solely in the ED setting.

In a prospective double-blind randomized controlled trial (RCT) investigating the benefits of vaccination of HCWs, Weingarten et al [17] found that vaccinating HCWs had no effect on sickness absenteeism or incidence of influenza-like illness although among those who developed clinical influenza, there was a nonsignificant trend toward fewer days of illness in the vaccinated group. However, in another RCT of 264 HCWs in 2 large teaching hospitals, Wilde et al

[18] found that influenza vaccination was effective in preventing serologically defined infection by influenza A and B, but it did not significantly reduce the cumulative days of febrile respiratory illness nor days of sickness absence. A double-blind RCT conducted in a children’s hospital in Finland also showed that the days of work lost because of Respiratory tract infections were significantly decreased in vaccinees, but the number of cumulative days of respiratory tract infections was unaffected [19].

Two prospective RCTs found that vaccinating HCWs in long-term elderly care hospitals resulted in reduction in mortality among patients [20,21]. However these 2 studies were potentially affected by selection and performance bias, as elaborated in a recent systematic review by Thomas et al [22]. It may not be strictly appropriate to generalize findings in elderly homes to other Clinical sites such as acute care emergency settings, and these studies did not investigate sickness absence of HCWs.

In a recent controlled trial comparing vaccinated with unvaccinated physicians (general practitioners) in Belgium, influenza vaccination was shown to protect against proven influenza among young general practitioners [23]. However, laboratory-defined influenza infection may have limited clinical significance and hence little significance in terms of economic impact if the number of days of sickness absence is not affected. Furthermore, evidence from Cochrane reviews already showed that there are modest benefits from vaccinating Healthy adults younger than 60 years; thus, any synergistic benefit from vaccinating young general practi- tioners (HCWs) has yet to be proven [22].

A retrospective cohort study conducted in a hospital setting in Japan found that the number of days absent from work is significantly less in vaccinated HCWs [24]. However, the study relied on self-reported number of days of sickness absence through questionnaires distributed to HCWs 2 months after the study period. The accuracy of this outcome measure was thus potentially affected by recall bias.

To the best of our knowledge, our study is the first to investigate the benefits of influenza vaccination of HCWs in an ED setting, based on an official staff record of sickness absence. Although the number of subjects in this pilot study was small, our results suggest that influenza vaccination of HCWs in this setting is significantly associated with a fewer number of HCWs requiring sick leave during the study period. Furthermore, although not reaching statistical significance, a trend was detected that the mean number of cumulative days of absence per person due to influenza-like illness is smaller in vaccine recipients. A larger prospective study is required to follow on these findings.

Our retrospective study has several major limitations, most of which being common to the studies mentioned previously, and some of these limitations have been addressed by the systematic review of Thomas et al [22]. The proof of association does not necessarily infer a cause- and-effect relationship. Even studies that are prospective RCTs using multivariate analyses may be limited by the difficulty in initially identifying, controlling, and addressing major confounding factors likely to influence the outcome. Subjects who volunteered for vaccination may also have other attributes to contribute to their protection from influenza. For example, these subjects are likely to be more conscious and careful about health and infection control measures such as hand washing and standard precautions. Likewise, the threshold for taking sick leave may be influenced by many factors and variables apart from the severity of influenza-like illness. An example of these variables is comorbid diseases. Finally, absenteeism due to influenza-like illness was identified only according to clinical presentation at the time of illness. Future prospective studies need to be planned such that laboratory confirmation of influenza infection is included.

In conclusion, although influenza vaccination of HCWs is widely advocated, evidence demonstrating its benefits is not strong and is based only on a few studies with definite limitations. Our study is encouraging for HCWs working in ED settings to follow recommended practice, and our findings may help ED managers in implementing vaccina- tion programs at a departmental level. However, more studies are required to verify our results. It is hoped that this pilot study and brief report could stimulate further research in the cost-effectiveness of influenza vaccination for HCWs and that these preliminary data can help plan further studies of this nature in the ED setting.

References

1. Centers for Disease Control and Prevention. Influenza vaccination of Healthcare personnel: recommendations of the Healthcare infection control practices Advisory Committee (HICPAC) and the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep 2006;55:1 - 41.
2. Talbot TR, Bradley SE, Cosgrove SE, et al. Influenza vaccination of Healthcare workers and vaccine allocation for healthcare workers during vaccine shortages. Infect Control Hosp Epidemiol 2005; 26:882 - 90.
3. Nicholson KG, Snacken R, Palache AM. Influenza immunization policies in Europe and the United States. Vaccine 1995;13:365 - 9.
4. King WD, Woodhandler SJ, Brown AF, et al. Influenza vaccination and health care workers in the United States. J Gen Intern Med 2006;21:181 - 4.
5. Burls A, Jordan R, Barton P, et al. Vaccinating healthcare workers against influenza to protect the vulnerable-is it a good use of Healthcare resources? A systematic review of the evidence and an economic evaluation. Vaccine 2006;8:4212 - 21.
6. Are your staff spreading disease to patient? ED Manag 1999;11: 103 - 4.
7. Wong SSY, Yuen KY. Influenza vaccination: options and issues. Hong Kong Med J 2005;11:381 - 90.
8. Taipianen T, Bar G, Schaad UB, Heininger U. Influenza vaccination among healthcare workers in a university children’s hospital. Infect Control Hosp Epidemiol 2005;26:855 - 8.
9. Canning HS, Phillips J, Allsup S. Health care worker beliefs about influenza vaccine and reasons of non-vaccination-a cross-sectional survey. J Clin Nurs 2005;14:922 - 5.
10. Poland GA, Tosh P, Jacobson RM. Requiring influenza vaccination for health care workers: seven truths we must accept. Vaccine 2005;18:2251 - 5.
11. Toy WC, Janosky JE, Laird SB. Influenza immunization of medical residents: knowledge, attitudes, and behaviours. Am J Infect Control 2005;33:473 - 5.
12. Harrison J, Abbott P. Vaccination against influenza: UK health care workers not on-message. Occup Med 2002;52:277 - 9.
13. Centers for Disease Control and Prevention. Interventions to increase influenza vaccination of health-care workers-California and Minne- sota. MMWR Morb Mortal Wkly Rep 2005;54:196 - 9.
14. Hughes QAM, Murphy E, Primrose WR. Factors influencing uptake of influenza vaccination among hospital-based health care workers. Occup Med 2004;54:197 - 201.
15. O’Reilly FW, Stevens AB. Sickness absence due to influenza. Occup Med 2002;52:265 - 9.
16. Abramson JH, Gahlinger PM. Computer programs for epidemiolo- gists: PEPI version 4.0. Salt Lake City, Utah7 Sagebrush Press; 2001.
17. Weingarten S, Staniloff H, Ault M, et al. Do hospital employees benefit from the influenza vaccine? A placebo-controlled clinical trial. J Gen Intern Med 1988;3:32 - 7.
18. Wilde JA, McMillan JA, Serwint J, et al. Effectiveness of influenza vaccine in health care professionals: a randomized trial. JAMA 1999;281:908 - 13.
19. Saxen H, Virtanen M. Randomized, placebo-controlled double blind study on the efficacy of influenza immunization on absenteeism of health care workers. Pediatr Infect Dis J 1999;18:779 - 93.
20. 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.
21. Carman WF, Alexander GE, Lesley AW, et al. Effects of influenza vaccination of health-care workers on mortality of Elderly people in long-term care: a randomised controlled trial. Lancet 2000;355: 93 - 7.
22. Thomas RE, Jefferson TO, Rivetti D. Influenza vaccination for health- care workers who work with elderly people in institutions: a systematic review. Lancet Infect Dis 2006;6:273 - 9.
23. Michiels B, Philips H, Coenen S, et al. The effect of giving influenza vaccination to general practitioners: a controlled trial [NCT00221676]. BMC Med 2006;4:17.
24. Ito Y, Sumi H, Kato T. Evaluation of influenza vaccination in health- care workers, using rapid antigen detection test. J Infect Chemother 2006;12:70 - 2.