Factors Associated with Seasonal Influenza Vaccination Among Nursing Staff of Three Teaching Hospitals Affiliated to Kerman University of Medical Sciences, Iran

Influenza is an acute viral infection of the respiratory tract with a high transmission rate that can lead to an epidemic and pandemic of the disease (1). The annual global infection rate of influenza is estimated by 5% - 10%, 20% - 30%, and 10% - 20% among adults, children, and the total population, respectively (2). Regarding 3 - 5 million severe cases and 290,000 - 650,000 deaths attributed to the disease, influenza is considered a public health threat and challenge. It is estimated that the economic burden of influenza is annually more than USD11 billion in the USA, imposing a considerable burden on the health system (3).

Influenza can affect all groups of a population; some subgroups, such as children, pregnant women, patients with chronic diseases, and the elderly, are more vulnerable and considered high-risk (2). Healthcare workers are at increased risk of exposure to influenza infection due to close contact with patients while providing health care services. Furthermore, the affected healthcare workers can transmit the disease to vulnerable patients and their families (4). They may be a reservoir of influenza for their patients and provoke nosocomial infection outbreaks among hospitalized patients, particularly those with underlying diseases (4).

Influenza vaccination is a key intervention to decrease the rate of morbidity, hospitalization, mortality, complications, and absenteeism related to the disease (5). Despite recommendations for influenza vaccination to healthcare workers by the World Health Organization, compliance with influenza vaccination by them is suboptimal worldwide, particularly in low -and medium-income countries (4, 6). Studies demonstrate a wide range of influenza vaccination rates across countries (7-9). A study reported influenza vaccination coverage among healthcare workers over 78% in the USA; however, another study found that less than 30% of their counterparts were vaccinated in European countries (7, 8). A study in 11 countries of the Eastern Mediterranean region reported the range of influenza vaccination rates from 1% in Pakistan to over 70% in Qatar (10). Several studies in Iran found a low coverage of influenza vaccination among hospital staff and other target groups (10-13).

Many factors at the individual and organizational levels are reported as motivators and barriers to influenza vaccination among healthcare workers (9, 10, 14). Demographic and personal characteristics, such as age, gender, educational level, occupational group, work setting, and work experience, were reported as factors influencing influenza vaccination in several studies (10, 14). Some studies found a relationship between uptake of the vaccine and knowledge and attitudes toward influenza and its vaccine among healthcare workers (6, 9, 15, 16). Results of many studies indicated other factors, such as misconceptions about side effects, the cost and availability, policies on the health system, and training, as determinants of compliance with influenza vaccination in healthcare workers (8, 15-17).

Although understanding the determinants of vaccine uptake is necessary to design a proper plan for promoting influenza vaccination, few studies reported factors influencing influenza vaccination among nurses in Iran (10-13, 18).

The present study aimed at assessing factors influencing influenza vaccination and reasons for accepting or refusing it among nursing staff of teaching hospitals affiliated to Kerman University of Medical Sciences in the Southeast of Iran.

The present case-control study was conducted on the nursing staff of three teaching hospitals affiliated to Kerman University of Medical Sciences from February to March 2019. The cases were selected from all nursing staff of the hospitals vaccinated against seasonal influenza in 2018. The case group was identified based on the influenza vaccination forms archived in the hospitals; moreover, the list of the vaccinated nursing staff of the hospitals was requested. The control group subjects were selected using a simple random sampling method from the lists of nurses who did not receive any vaccines in the same year. The number of participants in the control group was twice more than that of the case group, and the ratio was the same for the three hospitals. Nurses directly involved in patient care, with at least one year of working experience, were included in the study, but part-time nurses were excluded.

A questionnaire consisting of four sections was used for data collection. The 1st section included demographic items, such as gender, age, work experience, occupational group, marital status, and educational level. More items such as the workplace, underlying diseases, influenza vaccination of family members, receiving a recommendation for influenza vaccination in hospital, receiving education about the influenza vaccine, and intent on influenza vaccination in the next year, were also included in this section. The 2nd section had 11 yes/no/ I do not know items on influenza and its vaccine to assess the level of knowledge. The 3rd section had 12 items scored based on a five-point Likert scale (absolutely agree/agree/uncertain/disagree/absolutely disagree) to assess attitude toward influenza and its vaccine. The 4th section included items on the reasons for accepting or refusing influenza vaccination.

Content validity of the questionnaire was approved by an expert panel, including six experts in the disease prevention field. The content validity index was calculated as 0.82 and 0.86 for knowledge and attitude sections, respectively. A pilot study was performed on 30 nursing staff of the hospitals. The results of this assessment indicated the Kuder-Richardson coefficient for the knowledge and Cronbach’s alpha value for the attitude sections as 0.78 and 0.76, respectively. Exploratory factor analysis by the principal components method was used to confirm the construct validity. The result showed that the 11 items of the knowledge and 12 items of the attitude sections fell in two distinct factors. Factor loadings for attitude and knowledge ranged from 0.35 to 0.81 and 0.31 to 0.80, respectively.

In terms of scoring the knowledge section, incorrect and I do not know answers were given 0, and a correct answer 1; therefore, the possible knowledge score ranged from 0 to 11. Positive items of the attitude section were scored from 1 (absolutely disagree) to 5 (absolutely agree) and the negative ones reversely. Therefore, the possible score for each item and possible total score for the attitude section (summation of all items scores) could range from 1 to 5 and 12 to 60, respectively.

The questionnaire was completed by the participants. The study objectives and instructions to fill the questionnaire were provided for each subject. The questionnaires were completed after obtaining written consent. The study protocol was approved by the Ethics Committee of Kerman University of Medical Sciences (ethical code: IR.KMU.REC.1398.289).

Data were transferred to SPSS version 22. Descriptive results were expressed as mean, standard deviation (SD), and percentage. Independent samples t- and chi-squared tests were employed for univariate data analysis. Also, the binary logistic regression was used to determine the predictor variables of compliance with influenza vaccination. Accordingly, variables with P-values less than 0.2 in univariate analysis were used for regression modeling. A P-value of 0.05 was considered as the level of significance.

Out of 555 participants (185 vaccinated and 370 unvaccinated), 480, including 160 in the vaccinated and 320 in unvaccinated groups, completed the questionnaire; 35 questionnaires were excluded due to incomplete data (8 and 37 questionnaires in the vaccinated and unvaccinated groups, respectively). In the end, data of 435 respondents (overall response rate = 78.4%), including 152 in the vaccinated (response rate = 82.2%) and 283 in unvaccinated groups (response rate = 76.5%), were entered in data analysis. The mean ± SD and median age of the participants were 35.88 ± 8.64 and 37 years, respectively; 53% aged 36 years or above. The majority of the participants were female (87.7%), and more than three-fourths of them (76.7%) were married. Moreover, 74.7% of the participants were nurses, and the rest were nurse assistants. The educational level of 76.1% of all the participants was a bachelor or higher degree, and over 62% worked in the internal medicine wards. The mean ± SD and median work experience of the subjects were 12.17 ± 8.26 and 12 years, respectively.

Out of 1830 nursing staff of the hospitals, 185 received influenza vaccines in 2018, representing the vaccination rate of 10.1%. Gender was significantly associated with the influenza vaccination in the participants (P < 0.001); however, the frequency of females in the vaccinated group (75.0%) was lower than that of the unvaccinated one (94.6%). In terms of occupational group, the frequency of nurses in the unvaccinated group was higher than that of the vaccinated one (80.4% vs. 64.5%), while the frequency of nurse assistants was higher in the vaccinated group (35.5% vs. 19.6%). A significantly higher proportion of the unvaccinated ones (80.6%) had a bachelor or higher degree compared to the vaccinated group (67.8%) (P = 0.002). Moreover, the frequency of influenza vaccination in the family members was significantly higher among the vaccinated ones (50.3%) compared to the unvaccinated group (25.4%) (P < 0.001). The majority of vaccinated ones (80.1%) received a recommendation for influenza vaccination in hospitals compared to the unvaccinated group (54.8%) (P < 0.001). Furthermore, a higher proportion of vaccinated ones (78.8%), compared to the unvaccinated group (34.1%), reported an intent to uptake influenza vaccine in the next year (P < 0.001). There was no significant difference (P > 0.05) between the vaccinated and unvaccinated groups in terms of age, marital status, work experience, ward type, underlying diseases, and receiving an education about the influenza vaccine (Table 1).

Frequencies of the correct answer to knowledge items are presented in Table 2, indicating no significant differences for most items between the groups (Table 2). The mean ± SD score of knowledge of influenza and the vaccine among all the participants was 5.89 ± 1.87 (out of 11). The mean score of knowledge was significantly higher in the vaccinated group (6.23 ± 1.82) than the unvaccinated one (5.70 ± 1.88) (P < 0.001).

The mean ± SD and median scores of attitude toward influenza and the vaccine were 42.60 ± 7.17 and 42 (out of 60) among the participants, respectively. Also, the mean score of attitude in the vaccinated ones was significantly higher than that of the unvaccinated group (46.01 ± 6.67 vs. 40.81 ± 6.77) (P < 001). In addition, the median scores of 11 (out of 12) items in the attitude section was higher in the vaccinated group compared to the unvaccinated one (Table 3).

Binary logistic regression analysis was employed to determine influenza vaccination predictors, and the result of the Hosmer-Lemeshow test showed a goodness-of-fit for the model (P = 0.097). Based on the model, four factors, including gender, influenza vaccination of the family members, receiving a recommendation for influenza vaccination in hospital, and the score of attitude toward influenza vaccination, were the predictors of influenza vaccination among the nursing staff. Odds of influenza vaccine uptake was four times higher in males than females (adjusted odds ratio (AOR) = 4.77, 95% confidence interval (CI) = 2.13 - 10.64), and odds of influenza vaccination was 1.86 higher in nursing staff receiving a recommendation for influenza vaccination than the ones not receiving it (AOR = 1.86, 95% CI = 1.06 - 3.26). Also, odds of influenza vaccination increased 2.73 times in nursing staff whose family members received influenza vaccine (AOR = 2.61, 95% CI = 1.55 - 4.41). Furthermore, the model showed that one unit increase in the attitude score increased the odds of influenza vaccine uptake by 1.05 units (AOR = 1.05, 95% CI = 1.03 - 1.07) (Table 4).

As presented in Table 5, the most common reason for not receiving the influenza vaccine was the fear of vaccine adverse effects (64.7%), and more than one-third of the unvaccinated subjects cited the lack of trust in vaccine manufacturers (36.0%) as a reason for refusing vaccination. Moreover, three reasons were reported for refusing the vaccine in over one-fourth of the unvaccinated subjects as being healthy (29.7%), lack of effectiveness of the vaccine (29.3%), and not considering influenza as a serious and severe disease (26.1%).

The three most frequent reasons given for vaccine uptake were self-protection (79.6%), patient protection (73.0%), and family protection (72.4%). A recommendation for vaccination by hospital managers was cited by 43.4% of the vaccinated subjects as a reason for accepting it (Table 5).

The result of the present study showed that a high proportion (~90%) of the nursing staff did not have compliance with influenza vaccination. Studies conducted on healthcare workers of the Middle-East and most European countries revealed that the influenza vaccination rate was suboptimal; however, more than three-fourths of healthcare workers received the vaccine in the USA in 2017 (6, 9). In four studies performed in Iran, compliance with influenza vaccination among healthcare workers was 27.7%, 30.7%, 51%, and 57.7% (10-13). Some studies reported suboptimal adherence to preventive and therapeutic measures in patients and healthcare workers (19, 20). Suboptimal compliance with protective and personal safety measures may lead to some consequences, such as increased morbidity, mortality, and healthcare expenditure (19).

The present study showed a knowledge gap between influenza and its vaccine in the participants; however, the vaccinated nursing staff had a higher knowledge than the unvaccinated ones. Consistent with the present study, research demonstrated a positive relationship between knowledge level and influenza vaccine uptake in healthcare workers (9, 21, 22). Insufficient information and misconceptions about influenza and the vaccine were reported as primary factors influencing noncompliance with the vaccination in some studies (14, 23, 24). Increasing the knowledge of the disease and its vaccine leads to making an informed decision on the vaccination (25).s

The present study revealed that attitude toward influenza vaccination among the nursing staff was suboptimal but more positive in the vaccinated subjects than the unvaccinated ones. In line with the present study findings, several studies revealed that most healthcare workers had a negative attitude and incorrect belief in the influenza vaccine (9, 26, 27). A negative attitude toward the influenza vaccine was reported as the main barrier to vaccination (9). In addition, a proper understanding of the risk of the disease and a positive attitude toward safety, efficacy, and benefits of influenza vaccine are associated with a higher rate of adherence to influenza vaccination among healthcare workers (6, 28, 29).

The present study demonstrated that the fear of vaccine adverse effects was the most common reason (64.7%) among the nurses for refusing the influenza vaccination. A study in some Middle-Eastern and North-African countries reported that the fear of vaccine side effects was one of the main barriers to influenza vaccination in Algeria, Turkey, Libya, Lebanon, and Iran (9). Furthermore, the prevalence of fear of vaccine adverse effects as a reason for noncompliance with the vaccination in healthcare workers was reported in three studies in Iran as 14.3%, 23.1%, and 51%; in the present study, it had a considerable higher frequency (11, 12, 30). Awareness of vaccine safety may result in lower concerns about vaccine adverse effects and increased vaccine acceptance (6).

Mistrust in pharmaceutical companies was another reason for refusing vaccination against influenza. Consistent with the present study result, Freimuth et al. (31), found a low trust in vaccine manufacturers in the USA; lack of confidence in the vaccine, health system, and vaccine manufacturers were identified as factors influencing the refusal of influenza vaccination (31, 32).

Self-protection, patient protection, and family protection were the main reasons for influenza vaccine uptake in the vaccinated group; recommendations by the Ministry of Health were the reasons for vaccination only in 43.4% of the participants. Several studies, consistent with the present study, reported self-protection as the primary motivating factor of vaccination; however, there were inconsistencies with the present study results as patient protection was less motivating (22, 28, 33, 34). According to a review study, 23 out of 40 studies found that self-protection and family protection were the most common reasons for influenza vaccine uptake (35). Some authors stated that to improve vaccination coverage in healthcare personnel, highlighting self-protection and family protection as a personal gain is more effective than patient protection as a moral consideration or organizational regulation (33, 34).

The present study showed gender, occupational group, and educational level as the personal characteristics contributing to influenza vaccine uptake. Unlike the present study findings, studies in Iran did not report any differences in the influenza vaccination rate between genders (10, 11, 13). A review study found that sociodemographic characteristics, such as gender and age, were the most commonly reported factors for influenza vaccine uptake; however, the knowledge and attitude toward influenza vaccine and workplace conditions were more influential than sociodemographic factors (15).

To the best of the authors` knowledge, it was the first case-control study on factors contributing to the acceptance of influenza vaccine in Iran; however, self-selection bias may be a possible limitation of the study as the participants were more likely to have information about the influenza vaccine.