Determinants of vaccine hesitancy

Evidence suggests the determinants of vaccine hesitancy among healthcare staff include age, gender, comorbidities, and profession cadres, in addition to vaccination history.

Age and gender

Evidence from Italy^5-7, and Poland⁸ suggests the COVID-19 pandemic has positively influenced young HWs uptake of influenza vaccine. Italians aged <30 years showed an increased vaccination likelihood in 2019–2020⁵ and Polish HWs aged 31–40 years had an increased immunization willingness in 2020–2021⁸. This could be attributed to awareness campaigns, as well as the rising knowledge regarding the importance of influenza vaccination⁵.

There is consistent evidence among studies analyzed from Italy that males are more likely to accept influenza vaccination during the COVID-19 pandemic^6,7,9,10. Young (25–35 years) male HWs demonstrated the biggest leap in vaccine adherence during the pandemic⁶, where Italian male healthcare staff had higher positive willingness toward flu immunization compared to females (74.7% vs 62.5%, respectively)¹⁰. However, Costantino et al.¹¹ reported that ‘no significant differences’ exist between HWs’ genders.

Comorbidities

Evidence suggests that, in the context of the pandemic, healthcare staff with chronic diseases and comorbidities, defined here as hypertension, bronchial asthma, thyroid disorders, diabetes mellitus and rheumatic diseases, alongside sick HWs who are not on long-term medications¹², have higher vaccine acceptance and flu immunization rates particularly in the US¹³, Spain¹⁴, Czech Republic¹², and Cyprus¹⁵. This is evident in the Czech Republic, where flu immunization rates increased to 53.4% from 22.2%¹². Comorbidities associated with a higher risk for flu complications ultimately act a positive prediction factor for influenza vaccination¹³. Redondo Marguello et al.¹⁴ noted that chronically ill HWs aged ≥65 years had a positive perception of flu vaccine effectiveness and benefits.

HWs’ profession cadres

Research shows there has been an increase of influenza vaccine uptake amongst healthcare staff, in particular those within intensive care units (ICUs), due to the COVID-19 pandemic, particularly in Italy^6,7, China¹⁶, Czech Republic¹², and Greece¹⁷. For example, in China ICUs had increased rates of flu vaccination among HWs compared to other units (70% versus 58%, respectively)¹⁶. This is further corroborated by Perrone et al.⁷ who noted how flu immunization rates were highest within the specialist medicine department, followed by specialist surgery, and administration departments (34%, 13.6 %, and 13.1%, respectively).

Moreover, in the context of the pandemic, physicians were found to be more willing to get vaccinated for influenza compared to nurses, mainly in Italy^5,6, Poland⁹, Czech Republic¹², Cyprus¹⁵, and Greece¹⁷. For example, in Cyprus, for the 2019–2020 season, physicians had higher influenza vaccination rates than nurses or other HWs cadres (68.9%, 20%, 29.8%, respectively)¹⁵. However, a recent cross-sectional study reported that nurses’ refusal rate to seasonal influenza vaccination has declined in the COVID-19 context¹²; amongst Italian nurses there was a 28.1% rise in influenza vaccination rate⁶. A similar rise can be seen among paramedical personnel, such as radiology and radiotherapy, but in regard to attitude towards vaccine uptake, with +30.3% reporting a positive attitude towards influenza vaccination during 2020–2021⁶.

Non-physicians had a major concern of concomitant infection of influenza and COVID-19, specifically in Italy⁷ and Czech Republic¹². This is evident in the +308.3% increase in participation among administrative staff, during the 2020 influenza vaccination campaign in Italy⁷. However, there are studies that suggest the contrary: the only noticeable decline in influenza vaccine uptake was among health administrators^6,18. These studies showed a decrease of 3.2% in vaccination uptake among Italian administrative staff⁶, with Irish administrative staff reporting the lowest willingness for vaccination uptake¹⁸.

Vaccination history

There is evidence that the COVID-19 pandemic has increased the number of first-time influenza vaccine recipients particularly in Italy^5,6 and Czech Republic¹². For example, only 16% of the vaccinated Czech Republic HWs received seasonal influenza injections before the last season (2019–2020), and 25.2% of vaccinated Italian HWs got their first influenza vaccine in 2020–2021^6,12.

Healthcare staff adherence to influenza vaccination is associated with higher likelihood of influenza vaccination uptake amidst the COVID-19 pandemic particularly in Italy^5,10,11, Poland⁹, Saudi Arabia¹⁹, and Lebanon²⁰. Previously vaccinated HWs were 6 times more likely to get influenza vaccine than their counterparts²⁰. Scardina et al.⁵ revealed that a recent history of influenza immunization is the utmost variable for predicting influenza vaccine acceptance, which is ‘correlated with a higher influenza vaccine attitude score’.

The COVID-19 pandemic had a critical impact on the success of influenza vaccination campaigns mainly in Italy^5,6, Ireland¹⁸, and Lebanon²⁰. The majority of Italian HWs in 2020–2021 declared the necessity of influenza vaccination at the time of COVID-19 pandemic⁵. However, Bertoni et al.⁶ mentioned that 28.6% of Italian HWs had maintained their positive influenza vaccination status during 2019–2020 and 2020–2021 seasons; only 11.5% of those previously vaccinated did not get vaccinated in 2020.

Enablers of vaccine acceptance

A wide array of factors affects acceptance of influenza vaccines by healthcare staff. These include: HWs’ knowledge of influenza vaccine (n=6), HWs’ concerns to protect others (family, friends, patients) (n=7), healthcare staff self-protection (n=4), increased perception of risk (n=5), increased fear of COVID-19 infection (n=3), reduction of the burden on healthcare systems (n=4), the role of public health professionals and health authorities (n=4), increased confidence in influenza vaccines in the COVID-19 context (n=6), and vaccine availability (n=1).

Knowledge of influenza vaccine

Research from Italy^10,21, Cyprus¹⁵, Spain¹⁴, Saudi Arabia¹⁹ and Lebanon²⁰ has shed light on HWs’ knowledge on influenza vaccine as a determinant of vaccine hesitancy. Due to the high risk of infection associated with their job, healthcare staff have more knowledge regarding influenza immunization²¹. For instance, Di Giuseppe et al.¹⁰ mentioned that 96.1% of Italian HWs had knowledge about influenza vaccines from reliable sources such as scientific journals (56.5%), Internet (25.3%), and colleagues (20.4%).

Concerns regarding protection

Studies highlighted that, in the context of the pandemic, HWs’ concerns to protect others (family, friends, and patients) acted as a major motivator for influenza vaccine acceptance. This was evident in Italy^10,11, Cyprus¹⁵, Czech Republic¹², Poland⁹, Ireland¹⁸, and Lebanon²⁰. One study¹⁰ reported Italian healthcare staff’s sense of responsibility to prevent in-hospital spread of influenza in 2020. Another study¹⁸ noted how vaccinated Irish healthcare staff had concerns over family, patients, and colleagues’ protection.

HWs’ flu vaccination for self-protection was highlighted in four studies in Italy¹⁰, Poland⁹, Ireland¹⁸, and Cyprus¹⁵. In Italy, 81% of HWs reported self-protection as the reason for vaccination, with 98.1% in Poland, 79% in Ireland, and 77.4% in Cyprus^9,10,15,19.

The protection of themselves and their family was a stronger motive for vaccine uptake amongst female compared to male HWs^12,15. Male HWs noted that the main motivator was protecting patients, given their self-perception of the increased risk of catching influenza¹⁵.

Perception of risk and fear of COVID-19 infection

Increased perception of risk was reported in Italy^5,6,10,11 and Czech Republic¹². The COVID-19 pandemic was associated with a 50% increase in vaccination rates⁶, where the fear of spreading influenza was the main motivator for young HWs to get vaccinated¹². Notably, HWs who have never been vaccinated reported less fear of influenza infection compared with those who have been vaccinated before¹⁰.

Evidence from Italy⁶, Poland⁸ and Czech Republic¹² suggests the fear of COVID-19 infection had an influential effect on increasing the HWs’ acceptance of influenza immunization. The COVID-19 death toll contributed to the rise in influenza vaccine⁸. For example, 61% of Czech Republic HWs showed fear of having dual infections (influenza and COVID-19)¹².

Impact of influenza immunization

The impact of influenza immunization to reduce the surge of cases as well as the burden on healthcare systems¹⁰ and decrease staff absenteeism¹¹, has increased influenza vaccine uptake amongst motivated healthcare staff in Italy^6,10,11 and Lebanon²⁰. Approximately 80% of Lebanese HWs believed that influenza immunization would reduce ‘co-infection of influenza and COVID-19’, ultimately enabling ‘health services to better cope with COVID-19 complications’²⁰, and thus limit confusion associated with the differential diagnosis influenza-like-illnesses^6,10.

Confidence in vaccines

Public health professionals and health authorities have a critical role in boosting influenza vaccine adherence among healthcare staff particularly in Germany²², Cyprus¹⁵, Ireland¹⁸, and China¹⁶. For instance, 69% of vaccinated Irish healthcare staff found public health recommendations concerning influenza vaccine to be trustworthy¹⁸.

In the context of the pandemic, confidence in influenza vaccines has increased globally throughout Italy¹⁰, Poland⁸, Ireland¹⁸, Lebanon²⁰, Saudi Arabia¹⁹, and Iran²³; 66.3% of HWs deemed influenza a preventable infection, wherein concern (or lack thereof) regarding vaccine side effects acted as a predictor of willingness to vaccine uptake¹⁰. In Poland, Grochowska et al.⁸ stated that 62.5% of Polish HWs had increased confidence in influenza vaccination while 3.6% had more confidence in COVID-19 vaccines, and 26.3% trusted both vaccines equally. Eventually, 74.9%, 55.1%, and 53.3% of Italian HWs reported infection risk, vaccine effectiveness, and safety, respectively, for influenza vaccine adherence¹⁰.

Vaccine availability

Finally, policies securing on-site availability and convenient access to influenza vaccination are an important factor for vaccine adherence^15,16,22, specifically, availability of vaccines in work settings. Stepanek et al.¹² highlighted that Czech Republic HWs, especially those vaccinated in the 2019–20 season, had concerns on the shortage of influenza vaccines at their health facilities.

Barriers to vaccine acceptance

Evidence suggests that acceptance of influenza immunization is higher among healthcare staff with low perception of barriers to vaccination. In Lebanon²⁰, acceptance was approximately 4 times higher amongst healthcare staff with low perception compared with others. Barriers to influenza vaccine among HWs include: false perceptions, doubts and misinformation about vaccine safety, adverse events, effectiveness; insufficient time for vaccine uptake; confidence in natural or acquired immunity from previous infections; HWs’ work expertise and peers’ perspectives and attitude towards vaccination; lack of HWs’ knowledge regarding immunization; lack of trust in healthcare organizations, health authorities, and pharmaceutical companies; and concerns on vaccine availability, costs and needle injections.

Negative perceptions regarding vaccinations

Negative perceptions are found globally, in Italy^10,11,21,24, Poland (20%)⁹, Germany²², Cyprus¹⁵, Ireland¹⁸, Saudi Arabia (10.7%)²² and Lebanon²⁰. In Germany, in 2020–2021, perceptions on influenza disease and potential immunization adverse effects varied significantly ‘between vaccinated and non-vaccinated Emergency Department personnel’²². A similar trend was seen among Irish HWs, wherein concerns regarding side effects due to the influenza vaccine varied from 2018 to 2020–2021 (65% vs 30%)¹⁸.

Safety doubts, alongside fear from influenza vaccine-induced complications were particularly important barriers to vaccine uptake in Italy¹¹, Ireland (11%)¹⁸, Germany²² and Lebanon (18.21%)²⁰. For instance, 9.1% and 12.8% of Lebanese healthcare staff revealed concerns regarding immune system overload alongside potential allergies, respectively²⁰. However, it is important to note how all possible side effects due to influenza immunization, with the exception of injection pain, were higher among unvaccinated German HWs compared with their vaccinated counterparts for the 2020–2021 season²².

False perceptions pertaining to lack of vaccine effectiveness and efficacy were noted in Lebanon (7.86%)²⁰, Ireland (21%)¹⁸, Cyprus (21.5%)¹⁵, Saudi Arabia¹⁹, and Iran (21%)²³. In the Saudi Arabian study, 4% of HWs believed that influenza immunization could potentially cause influenza infection¹⁹. Moreover, confidence regarding influenza vaccine effectiveness was challenged due to perceptions of influenza as a non-dangerous ailment^10,21,24.

Insufficient time for vaccine uptake

Vaccine accessibility, specifically lack of time to go and get vaccinated, was a barrier in Italy²⁴, United States¹³, China (50%)¹⁶, Ireland (32%)¹⁸, Poland (30.4%)⁹, Spain¹⁴, Cyprus (3.4%)¹⁵, and Iran²³, indicating that this barrier is widespread. In Spain, the study found that 62% of physicians and 72% of nurses were unable to prioritize preventative measures, such as influenza vaccination, due to the workload¹⁴. This sentiment is echoed by Yi et al.¹⁶ who highlighted that busy schedules were responsible for the lack of immunization against influenza amongst Chinese healthcare staff in high-risk departments.

Confidence in immunity from previous influenza infections

Confidence in natural or acquired immunity from previous influenza infections was noted as a barrier to vaccination in Italy^10,11,24, Ireland (13%)¹⁸, Poland (17.8%)⁹, China (41%)¹⁶, Iran (33.8%)²³, Saudi Arabia¹⁹, and Lebanon (22.8%)²⁰. In Lebanon, 80.9% of healthcare staff regarded influenza as a mild infection, with additional few stating that the benefits of preventing influenza infection do not outweigh the barriers to vaccine acceptance and that immunization is not essential for healthy staff, 53.6% and 61.2%, respectively²⁰.

Work expertise and peers’ perspectives

Work expertise and peers’ perspectives greatly influence HWs’ decision regarding influenza vaccine uptake in China¹⁶ and Iran²³. The Iranian study found prior immunization experience, as well as negative feedback from non-vaccinated peers, ultimately enhanced HWs’ concerns regarding the development of side effects, in particular influenza-like symptoms²³.

Knowledge about vaccination

Lack of healthcare staff’s knowledge about vaccination is a barrier to influenza vaccine acceptance in Italy¹⁰ and Lebanon²⁰. In Lebanon, approximately 50% of HWs were not aware of the time frame for symptomology following exposure to influenza²⁰. Additionally, around 24% of Lebanese HWs were uninformed of the possibility of immunization during active virus circulation²⁰. Moreover, in Italy, approximately 54% of HWs were in need of further awareness of influenza immunization¹⁰.

Trust in organizations

Lack of trust in organizations or authorities, such as healthcare organizations, health authorities, or pharmaceutical companies, are an additional barrier to vaccine acceptance. This is particularly evident in Poland⁹ and Lebanon²⁰. Nearly half of Lebanese HWs did not deem information from official authorities as reliable and had concerns regarding potentially biased vaccine policies that prioritize the profit of pharmaceutical companies²⁰.

Vaccine availability

Evidence shows vaccine hesitancy is attributed to influenza vaccine availability, costs and needle injections in Italy⁵, Poland⁹, Ireland¹⁸, Lebanon²⁰, and Iran²³. Approximately 83% Lebanese and 25% Italian HWs reported concerns about insufficient vaccine availability, and unaffordable vaccine cost^5,20. Irish HWs expressed an aversion to the influenza vaccination injection site, or preferred to avoid needle injections altogether²³. Furthermore, nurses had more concerns regarding injections than physicians (10.7% vs 2.5%)⁹.

Barriers to influenza vaccine acceptance among HWs were common in all countries included in this review. A summary of enablers and barriers to vaccination are given Table 3.

Interventions for vaccine hesitancy

Interventions targeting influenza vaccine acceptance among HWs are ample and include: awareness campaigns, with dissemination of high-quality and transparent information on influenza vaccine, education and training targeting vaccine hesitancy; compulsory HWs’ influenza vaccination; promoting vaccine culture within workplaces; an incentives approach; and boosting vaccine affordability (defined as free-of-charge) and accessibility.

Awareness campaigns

Amidst the COVID-19 pandemic, awareness campaigns were the most popular intervention to increase influenza vaccine acceptance among HWs in Italy^5-7,10,11, Poland^8,9, United States¹³, Ireland¹⁸, Germany²², China¹⁶, Czech Republic¹², and Saudi Arabia¹⁹. Educational messages included scientific-based information about the influenza vaccine, such as safety, efficacy, and pros and cons, as well as promotional educational material such as posters and flyers^5,18.

Methods for awareness campaigns have extended to include compulsory sessions for HWs on influenza transmission¹⁸, implementing onsite influenza immunization promotion¹³, specific occupational counseling¹¹, sending informative emails and reminders⁵, and running promotional events before seasonal campaigns¹⁹. This is in addition to the strategy of relying on the ‘hospital internal network’ to disseminate data on influenza vaccines¹². Other methods to combat misconceptions regarding influenza vaccine are providing ‘educational handouts’ or arranging ‘lunch-and-learn activities’¹³.

Five studies discussed the importance of HWs’ education and training to reduce hesitancy towards influenza immunization in Italy⁵, Ireland¹⁸, Spain¹⁴, Saudi Arabia¹⁹, and Lebanon²⁰. For instance, a broad range of ‘information sources’ as well as conducting ‘seminars or training activities of scientific societies’ were preferred by physicians and nurses, respectively¹⁴.

Mandatory vaccination

In the context of the pandemic, of all the strategies targeting vaccine uptake, mandatory influenza vaccination for healthcare staff was one of the most controversial in Italy^10,11, Germany²², China¹⁶, Saudi Arabia¹⁹, and Lebanon²⁰. However, evidence shows that vaccinated healthcare staff are more likely to favor compulsory influenza vaccine policies²². In China, 84% of HWs approved mandatory influenza immunization provided that the vaccination was free-of-charge and conveniently accessible¹⁶. On the other hand, in Germany, unvaccinated HWs were likely to agree that ‘mandatory vaccination policies would be a reason to change jobs’ as well as noting that ‘it would be ethical to not go to work during an influenza pandemic’²².

Vaccine culture within workplaces

Studies emphasized the importance of promoting influenza vaccine culture in different workplaces in Italy^5,11, Ireland¹⁸, Poland⁹, Iran²³, and Saudi Arabia¹⁹. This encompasses the increase of vaccine availability by making influenza vaccines free-of-charge¹⁹, the immunization of decision-makers and leaders as an approach for vaccine advocacy^5,23, digital educational campaigns¹¹, and managerial and peer pressure¹⁸. Evidence seems to suggest that positive perception and attitudes towards influenza vaccination among young healthcare staff leads to an increase in older HWs’ influenza vaccine uptake¹¹.

Incentive approach

The incentive approach has also been utilized to increase influenza vaccine adherence in Italy⁷, the United States¹³, Ireland¹⁸, and China¹⁶. Incentives include cross-departments competition⁷, free-of-charge immunization¹³, or even vouchers¹⁸. For example, Chinese healthcare settings that incentivized influenza immunization among staff saw an increase in vaccine uptake (70% vs 39%, vaccine coverage among incentivized and non-incentivized, respectively)¹⁶.

Vaccine affordability and accessibility

In the COVID-19 context, evidence from Italy^5,7,10,21, United States¹³, Germany²², Ireland¹⁸, Poland⁹, China¹⁶, Iran²³, and Lebanon²⁰ shows how vaccine affordability (defined as free-of-charge) and accessibility are instrumental for HWs’ immunization adherence. In China, free-of-charge vaccinations are likely to increase influenza immunization adherence by 45%; 79% vs 34% coverage in free-of-charge and non-free-of-charge vaccination policies, respectively¹⁶. Additionally, in Germany, it has been suggested that the increased influenza vaccination coverage among the emergency department’s healthcare staff, during 2020–2021, was attributed to the COVID-19 pandemic²². This is thought to be due to the increased availability of immunization clinics on-site²².

Strengths and limitations

This review has limitations. First, it only included articles written in English. Nevertheless, there was a considerable number of publications on the topic of interest with the majority coming from non-English speaking countries. Thus, the studies included should be reasonably representative. Secondly, given the nature of the review (scoping, as opposed to systematic) – no quantitative analysis was performed, and we did not assess publication bias in the identified studies.

Nonetheless, strengths of the review lie in the narrative synthesis performed alongside identification of barriers. The latter can be addressed by policymakers in future pandemics.