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.
5.1. Conclusions
The current study results revealed that the influenza vaccination rate was suboptimal among the nursing staff. Also, there was poor knowledge and improper attitude toward influenza and its vaccine among healthcare workers. Furthermore, the present study found that male gender, receiving a recommendation for influenza vaccination in hospital, influenza vaccination of family members, and attitude toward influenza vaccination were the predictors of adherence to influenza vaccination. In addition, self-protection and patient protection were the common reasons for compliance with influenza vaccination, and fear of vaccine adverse effects and mistrust in vaccine manufacturers were the most common reasons for incompliance with it.