The potentially traumatic moral and ethical challenges that healthcare workers face in their occupation were first addressed in the moral distress literature. Moral distress has been conceptualized as the psychological distress that arises when a healthcare worker is prevented, by personal or institutional constraints, from doing what they believe to be right (e.g., witnessing the deterioration of patient care due to institutional factors or a lack of communication) (23, 24). Moral distress is associated with poor self-esteem, low job satisfaction, burnout and intention to leave one's position or profession (23–25). Relatedly, moral injury, as reviewed above, has been defined as a type of psychological response to trauma that may arise from exposure to a single or several potentially morally injurious events (PMIEs): rarely occurring, abnormally stressing, high-stakes situations with limited time for decision making (3, 26). Although a concrete definition has yet to be established, Litz et al. (10) contend that PMIEs can take several forms, including acting in ways that contravene moral values (i.e., acts of commission), failing to prevent events that transgress moral values (i.e., acts of omission), or witnessing someone else fail to act in line with moral values (10). Following this definition, PMIEs may be discussed as perpetration- and/or betrayal-based, where an individual holds perceived responsibility for a PMIE (e.g., by acting or failing to act), or has witnessed/been affected by the actions or inactions of others, respectively (11). Morally injurious outcomes will vary on an individual basis according to the codes of moral conduct in one's culture and one's personal values, yet the sequelae of moral injury, as reported in a recent integrative review, often include widespread effects in psychological/behavioral, social, religious/spiritual and biological domains (11). Following Litz and Kerig's heuristic continuum of moral injury (2), moral distress and moral injury may differ in frequency and event magnitude, where moral distress, although harmful, is believed to be less severe in degree of psychological impact when compared to moral injury (2). Due to its origin in the military literature, empirical research on healthcare workers' experiences with moral injury is limited in comparison to research on moral distress among this population. Indeed, in a recent scoping review, Cartolovni et al. (27) identified just seven articles examining moral injury among healthcare workers. Given the unique moral and ethical challenges present in the healthcare arena, exacerbated further by the COVID-19 pandemic, research in this area appears to be accelerating, with some researchers using moral injury and moral distress as interchangeable terms in healthcare during the COVID-19 pandemic (28).

Healthcare workers may be at an elevated risk for moral injury during the COVID-19 pandemic as they are more likely to be exposed to PMIEs at this time than, for example, civilians. Possible PMIEs discussed within the healthcare context during COVID-19 include having to take potentially life-saving resources from one patient in an attempt to save another patient's life, exposing individuals to the coronavirus because of failure in the screening process, witnessing healthcare managers poorly ration life-saving resources, or witnessing people living life unbothered outside of the hospital (26, 29). Indeed, preliminary findings from ongoing research in our group have revealed that Canadian respiratory therapists experienced intubating and proning patients over 90 years of age and “holding an infant while he passed away because COVID rules would not allow his mother in the room” as PMIEs. Critically, as the pandemic persists, moral injury and other mental health concerns are expected to remain, if not increase. Hines et al. (30) reported that healthcare workers in the United States showed stable symptoms of moral injury across the first 3 months of the pandemic (i.e., March to July 2020), occurring at levels similar to reports from military veterans upon return from deployment (31). Similarly to military populations, moral injury in healthcare workers during the pandemic has been associated with anxiety, depression, PTSD and suicidal ideation (32). Some caution is warranted in the interpretation of these findings, however, as moral injury is a relatively recent concept in the healthcare context and, to date, the clinical and research communities have not identified a highly-reliable, psychometrically-validated measurement tool for common use in this population.

Notably, as moral injury has been related to psychological/behavioral, social, religious/spiritual and biological harm (11), outcomes of moral injury among healthcare workers performing their duties during the COVID-19 pandemic may also vary across these domains. For example, in the case of a respiratory therapist comforting a dying infant in place of his mother, the respiratory therapist may experience impairing moral emotions of guilt, shame, anger or betrayal. The distress associated with this experience may, in turn, lead the respiratory therapist to withdraw from others, question prior beliefs of the world as a just place or experience a spiritual/existential crisis (11). Exposure to this event may be associated with physical manifestations such as decreased sensitivity to pain or stress-related illnesses, such as arthritis and PTSD, as found in prior research on outcomes of exposure to PMIEs (33, 34). Furthermore, exposure to these types of events may be associated with a sense of being “dirty” or shameful, thus contributing to a sense of being undeserving. Relatedly, such feelings of being “undeserving” have been recounted by healthcare workers in our research group's ongoing interviews during the COVID-19 pandemic where healthcare workers have shared that these feelings have limited their efforts to seek appropriate physical or mental healthcare and/or take breaks and rest periods from the healthcare environment.

Social support is a psychological construct referring to the emotional and instrumental care provided by those close in one's social circle, such as family or close friends (16). Whereas, seeking social support to deal with traumatic stress is a protective factor against PTSD (18), a perceived lack of social support is strongly associated with increased PTSD symptoms (60). The role of social support in mediating PTSD has been reported among many populations, including war veterans (19), survivors of childhood sexual abuse (20), survivors of violent crime (61) and nurses (21). Cieslak (19) investigated the role of perceived social support and self-efficacy in veterans' adaptations to distress. The results of this investigation revealed that greater received and perceived social support predicted high coping self-efficacy, which in turn predicted lower post-traumatic stress and depression symptom severity (19). Kerasiotis and Motta (21) investigated PTSD symptoms among nurses and found that nurses reported high levels of anxiety but did not reach clinically significant levels of PTSD, depression and dissociation. Here, social support was inferred to help nurses cope with work-related stressors (21). Finally, in a study investigating the specific types of perceived social support that mediated PTSD development in female survivors of childhood sexual abuse, self-esteem support was defined as “others' communications indicating that the abused individual is valued” (20) and was the type of social support that specifically mediated PTSD development in the sample. It is critical to acknowledge that while social support is a strong moderator of PTSD symptom development and maintenance, PTSD characteristically undermines relationships and support networks (62) as discussed above, making social relationships a key target for PTSD intervention. Moreover, PTSD is highly associated with disruptions in childhood attachment (47, 63, 64), rendering it potentially more difficult to form and sustain interpersonal relationships into adulthood.

Social support is thought to influence the cognitive appraisals of traumatic events in survivors of trauma. Specifically, social support may influence how one attributes their role in the traumatic event and their beliefs about the world (65). Cohen and Wills' (66) well-cited stress-buffering model posits that social support is a protective factor against the deleterious effects of trauma exposure as it increases one's perceived ability to cope with trauma and reduces negative appraisals of the traumatic event (22). In a study investigating social constraints, post-traumatic cognitions and PTSD among recent survivors of trauma, those who reported more social constraints (i.e., feeling unsupported, misunderstood or alienated when seeking support) reported more negative post-traumatic cognitions (67). Further, both social constraints and negative post-traumatic cognitions were related to a greater number of PTSD symptoms in this sample (67). These findings are in keeping with decades of research on the role of social support following exposure to trauma where a lack of social support continues to be a strong risk factor for developing PTSD (18, 22, 68). Further, individuals with strong social support are likely to recover faster than those who lack support (68). Indeed, in a recent meta-analytic review, Zalta et al. (22) examined the magnitude of the relation between social support and PTSD symptom severity, reporting a medium effect size across 148 cross-sectional studies and 38 longitudinal studies. The results supported the notion that greater levels of social support and lower levels of negative social reactions are related to lower levels of PTSD symptom severity (22).

Though not fully understood, the relation between social support and resilience documented in neurobiological literature may represent, in part, the mechanism through which social support moderates PTSD symptoms. The noradrenergic and hypothalamic-pituitary-adrenocortical (HPA) systems are implicated in both stress and resilience. Individuals with PTSD display dysregulated noradrenergic systems that fail to terminate the stress response after exposure to stressful stimuli (62). Individuals who report low social support display physiological and neuroendocrine responses, such as increased heart rate and blood pressure, that are indicative of a heightened reactivity to stress (69). Conversely, stress resilience is associated with the ability to keep the HPA and noradrenergic systems stable during exposure to stressful stimuli and terminated when the stimuli are no longer present (69). Social support is thought to influence both biological and environmental susceptibility to stress by acting on the HPA and noradrenergic systems, encouraging resilience (69, 70). As such, on a neurobiological level, social support may be a key factor in mediating the stress response as it promotes resilience.

Relatedly, the neurohormone oxytocin also plays a key role in stress regulation where social contact impacts the HPA axis to release oxytocin and in turn reduce stress (71–77). Indeed, studies using animal models have demonstrated that social contact is associated with oxytocin release (75–77). Furthermore, oxytocin release during or just after exposure to stressful events has been shown to regulate the HPA axis through the corticotropin-releasing factor (72, 78). Oxytocin's affinity for reducing PTSD symptoms may be related, in part, to its critical role in social bonding as oxytocin is known as the neurohormonal substrate of human affiliations, including parental, romantic and filial social bonds (79). For example, oxytocin release is implicated in maternal-infant social bonds such that oxytocin levels early in pregnancy and postpartum were related to maternal bonding behaviors such as positive affect, attachment-related thoughts and frequency of attending to the infant (80). Indeed, in a study investigating the therapeutic potential of intranasal oxytocin administration as a preventative measure for PTSD symptoms, Frijling et al. (81) found that repeated oxytocin administration reduced the development of PTSD symptoms among individuals who were recently trauma exposed. Furthermore, oxytocin has been shown to cause long-term depression of the amygdala, regulating the amygdala's sensitivity to aversive social stimuli (74). As such, the relation between social support and PTSD symptom severity may be explained, in part, due to the release of oxytocin, which is critical for social bonding and regulates the HPA axis along with subcortical structures critical to the stress response [see Lanius et al. (82) for a detailed review of the neurobiology of PTSD, including its dissociative subtype].

Research on healthcare workers' perceived social support during the pandemic is limited yet provides evidence that social support is critical for mental health and well-being. Indeed, in a systematic review of quantitative studies investigating psychological resilience, coping behaviors and social support in nurses during the pandemic (84), only seven studies explored the relation between social support and mental health outcomes, where greater perceived social support yielded a reduction in burnout (84, 85) and explained variance in psychological distress (84, 86). Using qualitative interviews, Brophy et al. (87) explored Canadian healthcare workers' experiences during the initial months of the pandemic, reporting that a perceived lack of support from employers affected healthcare workers' sense of well-being (e.g., a co-worker being sent to care for a suspected COVID-19 patient without PPE). Similarly, Xiao et al. (88) explored the impact of social support on sleep quality and functioning in a sample of Chinese healthcare workers providing medical care during the pandemic. Social support not only decreased anxiety and stress, but also increased self-efficacy in this sample (88). Finally, Labrague and De los Santos (89) examined the role of resilience, social support and organizational support on COVID-19-related anxiety among nurses working on the frontlines in the Philippines. Here, whereas social support was defined as assistance and protection offered by colleagues, managers, friends and family, organizational support was defined as the degree to which resources, reinforcement, communication and encouragement were offered to an individual by their organization (89). Both social and organizational support significantly predicted COVID-19-related anxiety among this sample, such that greater degrees of these supports were associated with lower degrees of anxiety (89).

In recent surveys of healthcare workers' needs during the pandemic, healthcare workers have highlighted their desire for social support. For example, Shanafelt et al. (90) asked healthcare workers about their main concerns during the pandemic, their needs from leaders and their perspectives on tangible supports. Healthcare workers' requests were summarized as follows: hear me, protect me, prepare me, support me and care for me. Healthcare workers desire clear assurance from their leaders that they, along with their families, will be supported emotionally, physically and socially while working on the frontlines on the pandemic (90). Specifically, healthcare workers shared a desire for their expert perspectives to be included in decision making, for their risk of infection to be mitigated, for appropriate training to treat critically ill patients, for support in dealing with extreme work hours and distress and for practical support such as food and childcare aid should they be infected (90). This call for support was echoed in a recent review by Heber et al. (91) who reported that public safety personnel (PSP) who, like healthcare workers, face novel stressors while working during the pandemic (e.g., greater risk of infection compared to civilians), may benefit from consistent support offered in the form of specialized mental health and preparedness training, frequent and transparent communication, strong leadership and team building, assistance in navigating quarantine and focus on self-care.

Altogether, social support mediates PTSD symptoms in a range of populations, perhaps through influencing cognitive appraisals of events by survivors of trauma (i.e., buffering patterns of common emotional response to trauma, enhancing feelings of connectedness) and likely enhancing resiliency on a neurobiological level [i.e., increasing the availability of neurohormones associated with stress reduction, in turn, regulating the HPA axis and critical subcortical structures associated with trauma and stress; (63–65, 67, 69, 70, 84). Given the relation between moral injury and PTSD symptoms and emerging mental health data suggesting that social support is important for decreasing healthcare workers' anxiety and stress during pandemic situations, targeting perceived social support is one means by which organizations and individuals may mediate the morally injurious outcomes for healthcare workers exposed to PMIEs during the COVID-19 pandemic. This may be accomplished by creating Communities of Practice where healthcare workers may gather in person and/or virtually to discuss shared concerns and coping mechanisms, or by ensuring that healthcare workers have regular breaks to spend with family members or creating “buddy systems.” Similarly, the need for efforts to retain a healthcare workforce that is increasingly considering leaving the profession given experiences throughout the pandemic (92, 93) combined with our own preliminary qualitative findings that healthcare workers demonstrate more concern for team members and family members than themselves, we suggest that efforts to retain healthcare staff and to promote workplace wellness focus, to an extent, on teams and team well-being. Strengthening these connections by highlighting social cohesion with team members may facilitate retention and promote post-traumatic growth. These efforts may also focus on the identity of the healthcare worker as a helping professional and serve as a reminder of why the healthcare worker entered the field in the first place.

Social acknowledgment involves receiving appreciation and positive reactions from the wider social environment in recognition of the difficult situation experienced by individuals exposed to trauma (16). The social environment may include colleagues, neighbors, authorities, clergy and the media (94). Social acknowledgment differs from social support as the former measures the degree to which one feels recognized and understood as a survivor of trauma and the latter emphasizes emotional or instrumental care (95).

Poor social acknowledgment (i.e., receiving disapproval and a lack of recognition as a survivor of trauma) is associated with greater severity of PTSD (95). For example, in a study examining PTSD symptom trajectories for Red Cross volunteers in Indonesia who responded to a large earthquake, those in the chronic PTSD trajectory reported lower perceived social acknowledgment compared to those in the resilient trajectory (96). Furthermore, a lack of social acknowledgment predicted increased PTSD symptomology in a longitudinal study on predictors of PTSD recovery in survivors of crime (97). In a study investigating trauma and PTSD symptomatology in German developmental aid workers, some participants reported that experiencing general disapproval from others was associated with more severe intrusive thoughts about the traumatic event and increased hyperarousal (94). Finally, a study on PTSD symptom severity, disclosure attitudes and social acknowledgment among Chinese and German survivors of crime found that, although PTSD symptom severity differed cross-culturally, disclosure attitudes and social acknowledgment predicted PTSD severity in both groups where a reluctance to disclose and a perceived lack of social acknowledgment predicted greater PTSD severity (97).

One mechanism through which social acknowledgment may mediate PTSD symptom development and maintenance is similar to that of social support, namely, post-traumatic cognitions. Post-traumatic cognitions are recognized as strong predictors of PTSD (97). Whereas, a strong sense of social acknowledgment may help survivors of trauma affirm positive cognitions that a traumatic experience has damaged, poor social acknowledgment may foster negative self- and other-focused cognitions (95). Indeed, Mueller et al. (97) found that perceived social acknowledgment was negatively associated with post-traumatic cognitions in a sample of 86 survivors of crime.

Here, it is critical to note evidence of altered patterns of response to emotions among individuals with PTSD that may pose as a barrier to the reception of social acknowledgment. For example, Nazarov et al. (98) found evidence for altered comprehension of affective prosody among women with PTSD related to chronic child abuse. Women in this study were asked to recognize angry, fearful, sad and happy emotions on a computer-based task and also asked to identify if the emotions portrayed in consecutive excerpts were the same or different. Nazarov et al. (98) found that women with PTSD took longer to identify all emotions except for those portraying anger in comparison to healthy controls. Interestingly, women with PTSD who experienced dissociative symptoms were more likely to be less accurate in discriminating between consecutive emotional presentations (98). Further, greater severity of childhood trauma was related to poorer accuracy in discrimination as well as slower recognition of emotions (98). Consistent with the altered patterns of emotional response demonstrated by Nazarov et al. (98), alterations in ToM, emotional recognition, empathic reasoning, moral reasoning and social behavior have been demonstrated among individuals with PTSD, as described above (15, 17, 43–45). As such, altered patterns of emotional response in PTSD must be considered when evaluating interventions targeting social acknowledgment.

Research on healthcare workers' perceived social acknowledgment during the pandemic is limited, with the majority of work instead focused heavily on social support from familiar others, such as co-workers. A small number of studies, however, have explored healthcare workers perceptions surrounding a lack of recognition for their efforts during the COVID-19 pandemic. For example, some healthcare workers have described feeling abandoned by political leaders and have attributed inadequate staffing and PPE during the pandemic to political leaders' poor response to their needs during the crisis (26, 99). Relatedly, in a recent systematic review and meta-synthesis on frontline healthcare workers' experiences during pandemics and epidemics (e.g., COVID-19, SARS, MERS, Ebola), Billings et al. (100) reported that workers felt abandoned and betrayed by organizations when they did not received promised financial renumeration for their service and sacrifice on the frontlines. Kröger (26) stated further that healthcare workers may perceive an inconsistent world outside of the hospital when witnessing people carelessly ignoring safety measures. Despite window decorations in homes and businesses thanking healthcare workers for their service, healthcare workers may perceive the non-chalance of people in their communities as a lack of recognition for their sacrifice on the frontlines. Finally, Cai et al. (99) investigated the psychological impact and coping strategies of healthcare workers in China and found that recognition from management and the government was associated with psychological benefit. Preliminary findings from our research groups' ongoing interviews with healthcare workers throughout 2021 corroborate the perceived lack of recognition discussed in the literature where nurses discussed feeling underappreciated at the beginning of the pandemic when financial renumeration for their service was smaller in proportion to that offered to some first responders. Unsurprisingly, we also heard from some healthcare workers that they felt abandoned and described a lack of recognition from the community when protests against masks and vaccines were held outside the hospital.

As social acknowledgment plays a role in the development and maintenance of PTSD symptoms in various trauma-exposed groups, it is imperative that healthcare workers perceive that they are recognized and understood as survivors of trauma during the COVID-19 pandemic. This perception may influence positive post-traumatic cognitions that may ameliorate moral injury as a response to COVID-19-related-PMIEs. Indeed, in outlining how healthcare workers desire strong leadership to support them during the pandemic, Shanafelt et al. (90) note the critical role of leadership asking healthcare workers about their concerns and acknowledging their requests. Despite potentially being constrained from providing answers, leadership must demonstrate that healthcare workers' service is acknowledged and appreciated (90). This call for strong leadership was echoed by Jetly et al. (1) who discussed key qualities of effective leadership in the military that may prove useful for leaders attending to COVID-19-related moral injury in healthcare workers. Jetly et al. (1) propose that effective leadership listens to the concerns of subordinates, are positive yet not overly optimistic, respect their subordinates' values, recognize that the risk of COVID-19 infection is not evenly distributed as frontline workers are the most vulnerable at this time, care about those whom they lead and accept the blame for team failures while attributing success to their team members.

Social exclusion is an act of ostracism related to stigmatization where one is rejected and isolated from a group (16). Humans have an inherent need for relationships with others that is disturbed in situations of social exclusion (101). Social exclusion may lead to feelings of isolation as if one were no longer viewed as a part of society (16). When ostracized, survivors of trauma may perceive themselves as less-human and believe that they are perceived to be less-human by the perpetrator of their ostracism (101). Social exclusion or ostracism can lead to physiological changes, such as cardiovascular issues or increased cortisol levels and psychological issues, including negative emotions of anger, sadness and shame (102, 103).

Individuals suffering from PTSD and other mental illnesses are often victims of social exclusion in the form of stereotyping and stigmatization (104). For example, among East-African conflict survivors, stigmatization was associated with an increased likelihood of PTSD after exposure to trauma (105). Wesselmann et al. (103) investigated the relation between perceived ostracism (i.e., “being ignored and excluded”) and post-traumatic stress among military veterans and found that perceived ostracism was related to post-traumatic stress symptoms, anxiety and psychological distress. Further, perceived ostracism explained variance in post-traumatic stress symptoms apart from theoretically relevant variables (i.e., deployment stress and social support) (103). In a study investigating the effects of social exclusion between individuals with PTSD and control participants, those with PTSD reported greater perceived social exclusion than control participants in an experimental manipulation of inclusion and exclusion (106), perhaps underscoring evidence of impaired social cognition among individuals with PTSD. Finally, among female adolescents exposed to war-related trauma, those who experienced sexual violence reported increased stigmatization (i.e., feeling treated worse than others, being insulted, rejected and excluded from family or community) (107). Further, stigmatization explained symptoms of depression and post-traumatic stress more so than did the direct impact of sexual violence in this sample (107).

Healthcare workers may perceive themselves to be socially excluded during the pandemic. In acknowledgment of the stigmatization that healthcare workers may experience by their communities during disease outbreaks, Taylor et al. (108) conducted a North American study evaluating non-healthcare workers' attitudes toward healthcare workers serving during COVID-19 and found that more than one quarter of respondents believed that healthcare workers should be subject to severe restrictions, including isolation from communities and families. Further, one-third of the respondents reported avoiding healthcare workers due to fear of infection (108). Indeed, Kröger (26) highlighted how healthcare workers have been prohibited from certain public spaces including bringing their children to school and Shimizu and Lin (109) recounted instances of defamation against healthcare workers in Japan during the pandemic. Individuals affected by COVID-19 in Japan have experienced societal rejection, discrimination and stigmatization and since healthcare workers are at a high risk of infection due to contact with COVID-19 patients, they are more likely to suffer from social exclusion (110). Reports indicate that Japanese healthcare workers have been victims of discrimination and abuse outside of work as the public treats them as “germs” (109). Healthcare workers in Japan have also been denied access to public transportation and their families have fallen victim to discrimination as well (109). In Canada, a national news organization reported on two nurses' experiences of facing criticism for crossing the border to provide care at a hospital in Detroit. The nurses described being blamed for bringing COVID cases into their city as they worked to be a part of the solution by caring for COVID-19 patients (111). Furthermore, Dye et al. (112) conducted a survey of healthcare workers' experiences of COVID-19-related bullying and stigma with participants from across 173 countries, reporting that healthcare workers were experiencing social exclusion during the pandemic, especially in communities affected by the intersection of racism, violence and police involvement (112).

In sum, social exclusion violates the inherent human need for relationships, consequently generating physiological and psychological disturbances. The effects of social exclusion in the form of stigmatization have been documented among various populations such as war veterans (103), survivors of sexual violence (107) and survivors of conflict (105). Our research group is currently preparing a scoping review on healthcare workers' and public safety personnel's exposure to PMIEs and distressing experiences during the pandemic. Here, we identified a need for further investigation of the verbal and physical abuse that healthcare workers have experienced in order to understand the context and severity of such exposures globally. As social exclusion is implicated in the development and maintenance of PTSD symptoms, targeting healthcare workers' perceptions of social exclusion may be an effective strategy to prevent and treat COVID-19-related moral injury.