Recent geopolitical events have led to a surge in human migration. The United Nations High Commission for Refugees (UNHCR) reports that in 2023, 117.3 million people were forcibly displaced worldwide, an increase of 8%, (8.8 million people) since 2022 – these numbers have been increasing yearly over the past 12 years [1]. This has revealed significant issues concerning the health of migrants, especially mental health and lack of access to adequate healthcare during the migration journey, and during integration in host countries [2].

Migration itself is an established social determinant of health, affecting the physical, mental and social wellbeing and overall health of refugees and migrants [3]. The migration process is dynamic and complex with challenges to health and wellbeing, as well as traumatic events that may occur across all phases - pre-migration, transit, and arrival and integration in the host country. Circumstances in the country of origin, such as political instability, conflict, and environmental factors influence migrants’ baseline health [3]. During the migration journey, lack of access to healthcare and exposure to traumatic events such as conflict, physical and sexual violence, detention, torture, discrimination, exploitation and loss or separation from family can further negatively affect mental health [4, 5]. In the host country, circumstances such as the political environment, discrimination, complexities associated with acculturation, fear of deportation and long waits for asylum application decisions can lead to a persistent state of unpredictability and uncontrollability of one’s life [3, 6, 7]. Financial hardship and economic stressors can augment these difficulties, as the worry of meeting basic daily needs contributes to a sense of uncertainty about the future [7].

Individuals who flee their country seeking legal refugee status are considered asylum seekers. After their individual situation has been assessed by the host country’s government, and it has been determined that there is a threat to safety due to persecution, armed conflict, or violence, they are given legal refugee status and considered refugees, as per the 1951 refugee convention [8]. Immigration from Eritrea and Somalia into Switzerland has been ongoing for the last 2 decades due to political and economic instability and climatic issues such as drought and floods [9–11]. In 2022, Eritreans and Somalis were the 3^rd and 6^th largest groups to submit applications for asylum in Switzerland [12] and over 40% of all refugees in Switzerland originated from Eritrea or Somalia, with Eritreans representing the largest group [13]. Migrants from the Horn of Africa to Europe typically travel along the northern migration route through Sudan, Libya and the Mediterranean. This route is associated with extreme risks, including arbitrary detention, torture, extortion, human trafficking, murder, sexual and other severe violence and death. It also involves the Mediterranean sea crossing, the deadliest migration route, where many drownings occur [10, 14, 15]. Psychological trauma experienced during migration, post migration stressors and triggers of prior traumatic experience can have significant and prolonged impact on mental health [4, 6].

The World Health Organization’s (WHO) review of global health data, along with several meta-analyses, show a high burden of mental health conditions among refugees and migrants, with reported prevalences of 32% for depression, 11% for anxiety and 32% for post-traumatic stress disorder (PTSD), although estimates vary across studies [6, 16, 17]. Evidence indicates that migrants -particularly asylum seekers and refugees- experience higher rates of depression, anxiety, PTSD, postpartum depression and psychosis than the general population [3, 6].

In Switzerland, studies similarly report substantial mental health needs. One investigation among refugees found rates of depression, anxiety and PTSD of 42%, 39% and 41%, respectively [18]. Another study focusing on recently arrived Eritrean migrants in Switzerland, reported prevalences of symptoms of depression, anxiety and somatic disorders of 15%, 10% and 10%, respectively, and nearly half of respondents screened positive for symptoms of PTSD (49%) [19]. Among migrants -including undocumented individuals- who had been living in Geneva for 5 years or more, prevalences of symptoms of anxiety (36%), depression (45%) and sleep disturbance (23%) were documented [20].

Harmful levels of alcohol and substance use have been observed among forced migrants [21]. Mental ill-health and harmful alcohol or substance use are closely intertwined [22]; alcohol may be used as a coping mechanism for trauma experienced before, during and after migration, but can also predispose individuals to further health risks, including liver cirrhosis and cancer [22]. Conversely, resilience has been shown to mitigate the effects of trauma and mental health conditions [23]. Only a few studies have investigated levels of resilience in migrants, including a study of Eritrean refugees in Switzerland, which found high levels of resilience in this population (60%) [19].

Despite the importance of mental health in refugees, there are few studies in Switzerland evaluating the prevalence of mental health conditions and/or their symptoms as well as substance use in refugees, especially in Eritrean and Somali populations [17–20, 24]. The reported findings vary by the type of questionnaires and the cut-offs used for assessments. Factors like mental health diagnostic criteria, migrant group (country of origin, type of migrant–asylum seeker, refugee, illegal migrant, labor migrant), host country and duration of residence there, socioeconomic status and integration policies play important roles [4, 6, 18, 25]. Consequently, the current landscape of epidemiological data concerning the mental health of refugees in Switzerland is limited and there is a clear need for robust evidence to inform migration health policies.

The study aimed to systematically assess the frequency of clinically relevant mental health conditions in Eritrean and Somali refugees beyond the early adaptation phase to inform migration health policies in Switzerland. Specifically, we determined the proportion of symptoms of PTSD, somatic disorder, anxiety, depression and unhealthy alcohol use as well as level of resilience in the Eritrean and Somali communities in Basel and Zurich, Switzerland. We hypothesized that mental health conditions, harmful or hazardous drinking and levels of resilience were substantially underappreciated in this population.

In this study, we determined the frequency of clinically relevant mental health symptoms and resilience in Eritrean and Somali refugees living in Basel and Zurich, Switzerland. In this study population with a longer integration period (median duration of stay after arrival was 8.4 years), we found low frequencies of moderate or severe symptoms of PTSD (7%), anxiety (0%) and depression (1%). However, there were elevated frequencies of symptoms of somatic disorders (18%) and harmful alcohol use (12%). The majority of refugees had high resilience scores (70%).

A comparison of our results to those of another investigation of Eritrean refugees in Basel who had recently arrived [19] reveal that the frequency of symptoms of mental health conditions in our sample were generally lower: PTSD (7% vs. 49%), anxiety (0% vs. 10.3%), depression (1% vs. 15%) and harmful alcohol use (12% vs. 18%). Although, a higher proportion of our study participants had high resilience scores (70% vs. 60%), the frequency of somatic disorders (18% vs. 10%) was higher in our study compared to the previous study [19].

There are various explanations for the differences in frequency of symptoms of mental health conditions in our study as compared to the study conducted by Chernet et al. [19]. First, the refugee’s duration of stay in Switzerland since arrival were remarkably different; in our study, the refugees had been living in Switzerland for about 9 years, whereas in the previous study, the refugees had only recently arrived (1–2 years). The duration of stay of our sample was relatively long because our study was conducted during the COVID-19 pandemic, when international border crossings were severely restricted. Subsequently, the number of new refugees arriving in Switzerland who could be recruited was severely limited. The refugee’s time since arrival can have a positive influence on mental health symptoms, as time allows healing from traumatic events [46]. We attempted an analysis of mental health symptoms by length of stay, but as only 11 individuals (11%) had been in Switzerland for less than 5 years, the analysis was not informative. In our study, we found that a large proportion of refugees had experienced traumatic events (32%), imprisonment (40%) and other difficulties (10%) during their journey. The study conducted by Chernet et al. [19], reported that 38% had been imprisoned and 58% had witnessed the death of a close person. Psychological trauma is one of the main causes of mental health conditions in refugees [47]. It is known that many refugees manifest severe mental health symptoms within the first years of arrival in the host country [48, 49]. Furthermore, in a subset of participants with shorter integration phases, who returned for follow-up 1 year later, most of the symptoms had decreased: anxiety (8% vs. 4%), depression (15% vs. 6%), PTSD (50% vs. 25%), except harmful alcohol use, which remained high (13%) [19].

During the first years of adaptation in Switzerland, refugees face post-migration stressors related to unemployment, integration, processing of the residence status, language and cultural barriers. These factors have an impact on mental health and may further worsen mental health symptoms. When compared to a previous study of shorter integration phases [19], our findings suggested a higher proportion of refugees with residence permits (97% vs. 42%) - this has been found to significantly benefit mental health in refugees, corresponding to their phase of integration [50]. Additionally, a higher proportion were employed (52% vs. 2%). As migrants spend more time in the host country and gain residence status they benefit from access to adequate healthcare, learning the local language and culture, all of which facilitate integration and finding employment. Another important factor for these refugees is that there is no violent conflict in Switzerland, and therefore this country offers a relatively good environment for mental health recovery. In our study, 51% of the population were married, compared to 31% in the study conducted by Chernet et al. [19]. The presence of a close partner can provide much needed psychological support when settling into a new environment. In addition, high resilience is associated with good mental health outcomes. The proportion of participants with high resilience scores in our study was much higher than in the Chernet et al. [19] study (70% vs. 60%). All these factors could further explain the higher frequency of symptoms of anxiety, depression, PTSD, and harmful alcohol use observed in the previous study [19].

The estimated prevalence of somatic symptom disorder in the general adult population is 5%–7% [51]. Somatic symptom disorders–i.e., when a person exerts such a strong focus on physical symptoms, that this results in major distress and/or problems functioning–are more prevalent in women in the general public, with an estimated female-to-male ratio of 10:1 [52]. This was true for our study as well with 29% of women reporting moderate to severe symptoms of somatic disorder versus 11% of men. The proportion of females in our study was much higher than that of Chernet et al. (39% vs. 11%), and the proportion of symptoms of somatic disorders was also higher (18% vs. 10%). The higher proportion of women in our study could explain the higher frequency of somatic symptoms [19].

Current evidence indicates that substance use among refugees appears to depend on the reason for migration as well as global and regional influences such as religious and cultural norms in both the country of origin and the destination country [21]. Furthermore, harmful alcohol or substance use has been documented in forced migrants and may be a coping mechanism for underlying trauma experienced during migration or related to living in a culture where alcohol is readily available, and its use is socially acceptable. The proportion of heavy episodic drinkers (harmful alcohol use) among the general population aged 15 years and above in Eritrea, Somalia and Switzerland are as follows: 5.6%, 0.3% and 36.2%, respectively [22]. A recent review indicated that hazardous/harmful alcohol use in refugees varied from 4% to 7% in community settings to 17%–36% in camp settings [21]. Our study results, which found harmful alcohol use of 12%, are slightly higher than that for community settings and the Eritrean, and Somali general population [22].

This study revealed a profile of elevated frequencies of somatic symptoms and harmful alcohol use among refugees after a relatively long stay in Switzerland. A study on the mental health of migrants, including undocumented migrants living in Geneva, Switzerland for ≥5 years revealed a profile of prevalent anxiety symptoms (36%), depression (45%), and sleep disturbance (23%) [20]. Though not directly comparable to our study due to different migrant populations and screening methods, it appears that a trend towards clinically relevant mental health symptoms may persist years after resettlement.

This study has several strengths and limitations. It is among the few studies investigating the symptoms of mental health conditions in long-term Eritrean and Somali refugee residents in the German speaking part of Switzerland. Recruiting migrants into health research is inherently challenging and low response rates are very common in such studies [53–57], leading to potential nonresponse bias- a limitation also relevant to this study. Many community members who were approached declined to participate, citing lack of time due to work commitments or childcare as well as mistrust of institutions and prior experiences of discrimination, well-documented barriers to migrant participation [53–55]. Because recruitment was conducted by community members approaching potential participants in public spaces, interactions were intentionally informal and conversational. When individuals declined participation, recruiters respected their decision without seeking further explanation or personal information. In this context, collecting data on non-responders would have been intrusive and risked eroding the trust that researchers had worked to establish within the community. Consequently, reasons for refusal were not systematically recorded and the potential influence of self-selection bias on prevalence estimates remains unknown. However, informal observations during recruitment suggest that some of those who declined to participate—particularly individuals expressing mistrust or those overwhelmed by work and childcare demands—may be underrepresented in our sample. Because such stressors are often linked to elevated psychological distress, their absence, and the resulting non-response bias, may have resulted in an underestimation of proportion of mental health symptoms in this population. Recruitment of this population required significant time, commitment, resources, and flexibility. Nevertheless, despite these challenges—and the added constraints of the COVID-19 pandemic—a considerable number of refugees agreed to participate, with a balanced distribution of males and females across age groups. The sample size was modest, particularly for Somali participants, and the number of refusals limits the generalizability of the findings. Finally, reliance on self-report questionnaires introduces the possibility of recall bias, which may also have contributed to underreporting of mental health symptoms.

In conclusion, we found that a significant proportion of Eritrean and Somali refugees experienced traumatic events during migration. Most of these refugees had been living for several years in Switzerland and had low frequencies of symptoms of PTSD, anxiety, depression and high resilience scores. However, they had elevated frequencies of symptoms of somatic disorders and harmful alcohol use. Trauma experienced during migration, post migration stressors and triggers of the traumatic experience during residence in the host country can have prolonged impact on mental health. Nevertheless, our results taken together with the existing literature, suggest that mental health conditions in refugees evolve over time, initially characterized by PTSD, anxiety and depression, and later shifting towards somatic disorders and harmful alcohol consumption. Our study highlights the need for long-term mental healthcare beyond the time of arrival in Switzerland to guarantee adequate health of the refugees. This study contributes to the understanding of refugee mental health dynamics after resettlement, providing evidence that the profile of mental health issues changes over time.