The COVID-19 pandemic, with the spread of the SARS-CoV-2 virus, has considerably impacted individuals' physical and mental well-being (1–3). The SARS-CoV-2, causing the illness coronavirus disease 2019 (COVID-19), can result in somatic symptoms such as cough, sore throat, fever, and myalgia (4), and in severe cases result in death (5). Mental well-being can be affected due to factors such as fear of infection, fear of dying, and a sense of helplessness (3), as well as by spread-related restrictions such as isolation and quarantine (6, 7).

When the incidence of psychological symptoms was investigated during initial (during the year 2020) and middle (during the year 2021) phases of the COVID-19 pandemic, the prevalence rates for depression, anxiety, and stress were found to be around 30% (3, 8). These prevalences can be compared with the 12-month prevalence reported before the COVID-19 pandemic, which was 6.9% for depression and 14% for anxiety (9), indicating that symptom levels did increase during the pandemic. Consistent with these findings, Pieh et al. (10) reported elevated levels of depressive, anxiety, and insomnia symptoms during the pandemic relative to pre-pandemic baseline levels. However, it is difficult to estimate how and to what extent individuals' mental well-being was affected during the pandemic. In their systematic review, Alqahtani et al. (1) concluded that depression, anxiety, and stress increased during the COVID-19 pandemic, but that the prevalence of these three conditions varied depending on region and other factors. For example, the prevalence of depression reported in the studies reviewed by Alqahtani et al. (1) ranged from 14.6% to 45%. For anxiety, the prevalence ranged from 8.3% to 47% (1). This heterogeneity is in line with earlier research regarding the impact on individual mental health during former phases of the COVID-19 pandemic. For instance, Mahmud et al. (11) showed that the prevalence of various psychological symptoms and conditions differed between studies focusing on various populations, regions, and time periods. Overall, it can be stated that individual mental health was adversely affected to some extent (1, 12), even among those who were not infected with the SARS-CoV-2 virus (13). Elevated levels of psychological symptoms have furthermore been reported to persist even in the later phases of the COVID-19 pandemic, when societal restrictions imposed due to the pandemic had been largely lifted (14).

Deng et al. (15) investigated mental health in those infected by the SARS-CoV-2 in a systematic review. They reported pooled prevalence estimates for depression, anxiety, and sleep disturbance of 45%, 47%, and 34%, respectively. No gender differences were found (15). A considerable number of people who have recovered from the acute phase of COVID-19 experience persistent symptoms that impair their daily activities beyond the initial illness (16, 17). This has led to the description of a post-COVID syndrome, defined as symptoms that develop during or after a COVID-19 infection, persisting for more than twelve weeks, and cannot be attributed to another diagnosis (18). Common symptoms reported are fatigue, dyspnea, sleep disorder (19), as well as cognitive dysfunctions such as concentrating difficulties, short-term and general memory loss, and impairment of executive functions (20). As with the general population during the COVID-19 pandemic and those being infected by the SARS-CoV-2, a significant number of post-COVID syndrome patients also report psychological symptoms, such as depression, anxiety, and post-traumatic stress disorder (20).

Internet-based cognitive behavioral therapy (ICBT) has been investigated as an alternative, or complement, to CBT face-to-face (21). ICBT is cost-effective when including weekly support by a therapist (22), not requiring as much therapist time as CBT face-to-face. At the same time, ICBT, when therapist support is included, has been shown to yield effects comparable to face-to-face CBT (23). There is also evidence supporting the effectiveness and acceptability of ICBT in routine clinical settings (24). ICBT can be delivered in various formats, such as with or without therapist guidance, and as either a standardized program applied uniformly to all participants or as an individually tailored intervention. In many studies, therapist-supported ICBT has demonstrated superior outcomes compared to unsupported formats (25), although self-guided treatments also have shown to yield clinically significant effects (26). Tailored ICBT, in which modules are chosen depending on the individual's specific symptoms and situation, has been found to be effective for depression and anxiety symptoms, as well as quality of life (27, 28). The treatment may consist of a selection of so-called treatment modules, which commonly address various typical CBT strategies such as behavioral activation, exposure, and emotion regulation, and can also focus on different areas, such as stress or perfectionism (27). The modules are typically text-based, with associated exercises, but may also include explanatory images or videos (29). With an individually tailored intervention, different sets of symptoms and comorbidity can be addressed (30). This is because the individually tailored approach allows individuals to undergo the same overall treatment program while receiving different content based on their psychological needs and symptoms. In contrast to non-tailored ICBT, where all participants work through the same treatment material, the tailored format offers flexibility by allowing the treatment components to be assembled in a modular fashion. Thus, rather than delivering a fixed set of treatment modules to all individuals, different modules can be provided in varying sequences depending on individual needs (27). People have been affected by the COVID-19 pandemic in different ways (1), which motivates an individually tailored ICBT approach.

During the COVID-19 pandemic, several trials were conducted investigating the effects of ICBT. Komariah et al. (31) examined the effects of ICBT during the pandemic in a systematic review and meta-analysis, including nine randomized controlled trials (RCTs). The trials varied in treatment format, including the focus of the intervention and the type and frequency of therapist support. Even if all studies targeted psychological symptoms related to the COVID-19 pandemic, the trials varied somewhat in terms of psychological symptom focus, e.g., depression and anxiety (32), only worry (33), only depression (34), and health anxiety (35). All trials shared the same target group, namely adults experiencing psychological symptoms related to the COVID-19 pandemic, except for one study (36), targeting COVID-19 patients. Aggregated results demonstrated ICBT as effective in reducing depression and anxiety symptoms during the COVID-19 pandemic, even if the studies differ in many aspects. Therapist-guided ICBT interventions included in the meta-analysis were shown to be superior to self-guided regarding the decrease in depression symptoms from pre- to post-treatment measurement (31). These results align with results displayed before the COVID-19 pandemic, showing that ICBT with therapist support is more effective than ICBT without (37). Regarding anxiety symptoms, however, the results were the opposite, showing self-guided ICBTs being superior to therapist-guided ones (31). When Mahoney et al. (38) investigated the effects of ICBT on symptoms of depression and anxiety before and during the initial and middle phases of the COVID-19 pandemic, no differences were shown, and thus, they concluded that ICBT remains effective in a pandemic context.

Additional studies on ICBT have been conducted during the COVID-19 pandemic, with somewhat conflicting results compared to those reported by Komariah et al. (31). For example, no significant effects on symptoms of depression and anxiety were found when Brog et al. (39) investigated a three-week-long internet-based self-help intervention aiming to target psychological distress related to the COVID-19 pandemic. These results differ from those found by Wahlund et al. (33), when they investigated a three-week-long self-guided treatment. Significant reductions in worry related to the COVID-19 pandemic and depression symptoms were shown in their study (33). Overall, trials investigating ICBT during the COVID-19 pandemic indicate that ICBT has potential. Still, the results differ to some extent (e.g., 33, 39), implying a need for further research within this area. Also, to the best of our knowledge, most of the ICBT trials have been conducted in the early phases of the COVID-19 pandemic (e.g., 33, 36, 40, 41), with only a few carried out during its mid-phase (e.g., 42, 43). During the pandemic's final phase, many people were vaccinated (44) and had been infected by SARS-CoV-2 at some point, resulting in a lower risk of somatic illness in case of infection and spreading of the virus in total and, thus, fewer restrictions prevailed than in the pandemic's former phases. However, this does not necessarily mean that the impact on the mental health diminishes (14). While many had the opportunity to return to a somewhat “normal” state, the pandemic's aftermath, for instance in terms of social contacts, was still current for some people. Thus, a need for psychological interventions in relation to the pandemic could still exist. Although other forms of internet-based psychological treatments exist and have been shown to be effective for depressive and anxiety symptoms among others, such as psychodynamic (45) or interpersonal (46) interventions, it is to our knowledge internet-based interventions with a CBT approach that have been most extensively studied during the COVID-19 pandemic. Thus, we aim to expand this area of research. Whether ICBT would be effective and feasible during the pandemic's final phase, as in its early and middle phases, is still relatively unexplored.

Taken together, the mental health during the COVID-19 pandemic has worsened in different areas (1), both in people infected by the SARS-CoV-2 (15) and not (13). ICBT has been investigated but, to our knowledge, not during the final phase of the pandemic. This study aimed to examine the feasibility of individually tailored ICBT with weekly support by a therapist during the final phase of the COVID-19 pandemic. The pandemic was still ongoing during this period, but many people were slowly transitioning back to “normal”, i.e., returning to their everyday life and lifestyle before the outbreak. At the same time, psychological symptom levels remained elevated relative to pre-pandemic baselines (14), and not all had the opportunity to go back to a “normal”, pre-pandemic, state. Thus, we aimed to evaluate whether ICBT, a psychological treatment that does not increase the risk of infection spread, can be effective for psychological symptoms that emerged or were exacerbated in relation to the COVID-19 pandemic and its consequences.

This study aimed to investigate the feasibility of an eight-week individually tailored ICBT with weekly guidance during the final phase of the COVID-19 pandemic. It was planned to be an RCT, comparing a treatment group with a waitlist control condition. However, we decided to switch to a within-group design due to recruitment issues and the low number of included participants. Out of the 25 individuals who went through the pre-treatment screening, 24 were included, and 15 completed the post-treatment measurement. Three participants explicitly expressed their desire to withdraw from the study during the treatment period. Out of eight assigned modules, the participants completed an average of 3.96 modules. Comparing pre-treatment and post-treatment estimates of various psychological symptoms using self-assessment questionnaires, results revealed significant decreases in depression and anxiety. Significant decreases were also found for some secondary outcomes (symptoms of health anxiety, fatigue and exhaustion, post-traumatic stress, loneliness) but not for others (stress, quality of life, experiences of cognitive functioning, financial stress and well-being). Knowledge about CBT principles was found to increase, as well as insomnia symptoms (even if the robustness test did not show increases in insomnia). Overall, the findings indicate that ICBT is feasible as a treatment for psychological symptoms during a pandemic, and more specifically, was feasible during the end of the COVID-19 pandemic. However, some adjustments to the treatment would be beneficial and necessary to improve and investigate further, to ensure its effectiveness.

This study was conducted to assess the feasibility of the ICBT in the late COVID-19 pandemic. The outcome analyses showed that symptoms of depression, anxiety, post-traumatic stress, healthy anxiety, loneliness, fatigue, and exhaustion, measured with the BDI-II, the GAD-7, the IES-6, the SHAI-14, the UCLA-LS-R, and the KEDS-9 respectively, had decreased from pre- to post-treatment measurement with medium to large effect sizes. Scores on the knowledge test about CBT, both raw and weighted, increased. Robustness tests showed the same results, except for the KEDS, which was not statistically significant. Thus, effects on primary and some of the secondary outcome measures were shown. The results are in line with earlier studies of ICBT conducted before (72) and during the COVID-19 pandemic (31), which show symptom reduction associated with ICBT, and an increased knowledge about CBT (65). The modules in the treatment included typical CBT strategies, but the content was adapted to fit problems related to the final phase of the COVID-19 pandemic. Regarding the primary outcome measures, symptoms of depression and anxiety, the results are consistent with previous findings from studies evaluating most of the treatment modules used in this study (40, 42). These findings further strengthen the evidence that ICBT, including weekly therapist support, can be beneficial not only at the onset (40) or during the middle phase of the COVID-19 pandemic (42), but also in its final phase. The results also suggest that the individually tailored approach, where participants receive treatment plans consisting of different modules with varying focus, combined with weekly support from a therapist, is feasible in a pandemic context. Module selection was based on a combination of the research team's clinical judgment and the participant's own preferences. These approaches have previously been tested both independently and comparatively, demonstrating effectiveness in reducing depressive symptoms, as well as symptoms of anxiety and quality of life (27). Furthermore, consistent with previous studies (65, 73), an increase in CBT knowledge was identified post-treatment compared to pre-treatment. It is relevant to further investigate CBT knowledge and its development in the context of ICBT, as this treatment format, through its psychoeducational content, may be regarded as a form of patient education and may provide insights into the educational component of the intervention. Overall, the findings indicate that individually tailored ICBT remains a relevant and beneficial intervention even in a global context different from than the one we are accustomed to, such as during a pandemic. The combined approach to module selection, balancing clinical assessment and participant preference, appears to be a viable method for heterogeneous psychological symptoms in times of a pandemic, and potentially other societal transitions.

Except for the effects on fatigue and exhaustion, the results appear to be robust despite the small number of participants and, in that sense, low power. During the COVID-19 pandemic, several previous studies have reported findings regarding transdiagnostic ICBT being effective for depressive and anxiety symptoms (e.g., 35, 38, 74). These transdiagnostic interventions are comparable to the individually tailored ICBT employed in the present study, as the treatment is designed to be applicable to individuals with a wide range of symptoms. In addition to the inclusion of standard CBT strategies in the treatment content, several other factors may contribute to the perceived helpfulness of ICBT. The therapeutic alliance, as in traditional face-to-face therapy, between the participant and the therapist may be important (75), as well as the participant's perceived alliance with the treatment program itself (76). Unfortunately, perceived alliance with the therapist or the ICBT program was not assessed in the present study. Furthermore, when comparing ICBT interventions, it is essential to consider that they often differ in several aspects, including the specific content of interventions (despite being grounded in CBT principles), the presence or absence of therapist support, as well as the overall duration and intensity of the treatment. An additional challenge when comparing ICBT studies conducted during the COVID-19 pandemic is that they were carried out at different phases of the pandemic. There is a considerable variation in the studies conducted, with a range from a brief, self-guided ICBT intervention conducted over three weeks at the beginning of the pandemic (33), to a therapist-guided nine-week intervention implemented during the mid-phase of the pandemic (74). Nevertheless, both approaches demonstrated significant effects on symptoms of anxiety and depression. Thus, despite differences and present challenges for cross-study comparisons, ICBT appears generally to be an effective treatment option for psychological distress during the COVID-19 pandemic (31, 38).

However, it is essential to emphasize that the results in this study were not compared against a control group, which means that other factors, such as the pandemic coming to an end or individual life events, may have impacted the results. Insomnia symptoms, measured with the ISI, did significantly increase during the treatment period, but this was not significant with the robustness test. Systematically, increased insomnia symptoms have, to our knowledge, not been shown during an ICBT, and one of the modules had sleeping problems as a focus, even if not all participants worked with it. It is unclear why the insomnia symptoms increased. No other symptom estimates showed an increase, but if this result reoccurs, it should be further investigated.

Results were non-significant on some of the secondary outcome measures; the BBQ, the PSS-14, the CFQ, and the IFDFW, aiming to measure quality of life, stress symptoms, experience of impairment in memory, perception, and motor function, and financial stress/well-being, respectively. In addition to the risk that this could be due to insufficient power, the treatment did not include modules that focused on all these specific areas, such as experienced cognitive dysfunction. However, there was a module about stress and one on financial stress, but not all participants were assigned these modules. In fact, only two participants completed the module Stress management, and only one completed the module about Managing financial stress. Possibly, a longer treatment period might have been needed for a more noticeable difference in these kinds of symptoms, such as experienced financial stress. Additionally, the treatment could have focused more on somatic issues, such as mental fatigue or pain, which might have had different effects on quality of life, given the number of participants probably having post-COVID syndrome. Nevertheless, there are other examples of ICBT during the COVID-19 pandemic that did not demonstrate significant effects on perceived quality of life among participants without post-COVID syndrome (74). An increase in quality of life between the pre- and post-treatment measurement, measured with the BBQ, was found to correlate significantly with the number of completed modules (r = .615). However, determining cause and effect is difficult. As work in the treatment progresses, quality of life may improve, but the ability to work with and complete modules might also partially depend on the experienced quality of life, corresponding to possibly a bidirectional association.

The ICBT investigated was individually tailored, meaning that participants received different modules with different focuses and CBT strategies, depending on their described symptoms. This aligns with the fact that people were affected by the pandemic in different ways (1), as well as with what Treanor et al. (77) concludes in their review about ICBT, that “one size does not fit all”. However, there was a significant difference in education level between those who completed the post-treatment measurement and those who did not, with more completers having an education at a college or university level than the non-completers. Although there could be several reasons for this, a reasonable hypothesis is that the ability and habit of processing text might influence whether a person completes the post-treatment measurement and the treatment in this study, which is primarily delivered via text. While this aligns with previous ICBT studies (78), it may be essential to consider that participants could suffer from cognitive impairments, such as concentration difficulties or mental fatigue, as a result of COVID-19 infection (19, 20). Three participants explicitly stated that they no longer wanted to be part of the study, mainly due to the amount of text in the treatment and because they did not have the energy or time to work through the material. These findings are important for evaluating the feasibility of the ICBT intervention, as well as for identifying which individuals it may, and may not, be suitable for and the underlying reasons.

The mean adherence, in terms of completed modules, was approximately half (3.96 out of 8). This suggests that many participants, given the current format of the modules, do not engage with, or at least do not actively work through, all the material included in the intervention. Although this observation does not differ substantially from previous studies on ICBT conducted during the COVID-19 pandemic (40, 42) or before the pandemic (79), the relatively low adherence may suggest a need for adjustments to the treatment format. In the future, the treatment and the accompanying module texts could be shortened to potentially facilitate the uptake or include both longer and shorter versions of each module, allowing participants to choose a version based on their needs and preferences. One challenge in doing so is determining which content and exercises should be prioritized, as the current treatment material consists of interconnected components, each with an intended purpose. To investigate this, focus groups could be employed, allowing participants to engage with the modules and subsequently provide feedback on which components they found most helpful and which they considered less central. Individual interviews or a survey could also be conducted to investigate participants' experiences regarding which aspects of the treatment were helpful and useful, and which were not.

Sixteen of the 24 participants were assessed as probably having post-COVID syndrome, and the majority of those who completed the post-treatment measurement (ten out of 15) were participants assessed as probably having post-COVID. These were the participants whose data were included in the analysis of treatment outcomes. There are indications that CBT for fatigue in the context of post-COVID may be helpful (80), although the body of research on psychological interventions for post-COVID, both in terms of feasibility and treatment effects, remains limited (81). Even if there is a risk that a text-based treatment, such as ICBT, can be difficult for people with fatigue or other cognitive impairments caused by post-COVID syndrome, another possibility is that text-based modules could for some people be more accessible and usable, since they can read at their own pace and revisit the material without any limitations. This is a contrast to face-to-face treatment, which is primarily verbal, as verbal language is ephemeral. Additionally, the possibility of conducting psychological treatment from home, as enabled by ICBT, could be advantageous for individuals with post-COVID syndrome, or others experiencing somatic symptoms such as pain (82). This positions ICBT as a treatment modality with the potential to reach a wide range of patients (80).

This study's dropout rate was 37.5%, meaning that nine out of 24 participants did not complete the post-treatment measurement. Carlbring et al. (72) noted in their meta-analysis that dropout is expected in CBT and ICBT studies. However, the calculated dropout rate from the meta-analysis was 15.7% (72), which is lower than the rate in this study. Meanwhile, another study of dropout rates by Schmidt et al. (78) estimated the average rate within ICBT for depression to be 32%. Similarly, van Beugen et al. (83) reported a median dropout rate of 29% in ICBT for chronic illness, although the reported range was broad (2%–57%). It is important to acknowledge that these studies were conducted before the outbreak of the COVID-19 pandemic, and that dropout tendencies may differ during and after the pandemic. To the best of our knowledge, dropout rates in ICBT during the final phase of the COVID-19 pandemic have not been specifically investigated and, thus, partly provide the rationale for conducting a feasibility study. Dropout rates during the COVID-19 and other pandemics require further investigation, as well as the reasons for dropping out and the treatment experiences of these participants.

There are several possible reasons for our difficulties in recruiting participants. The study and the recruitment phase were in line with its purpose in the late COVID-19 pandemic, when many were possibly quite tired of the pandemic and were trying to return to some “normal” state, i.e., to the pre-pandemic life and habits. The project's name, PostCoronaCope, could also have been quite unclear and misleading, indicating that the study and treatment were targeted towards post-COVID syndrome, even if no inclusion criteria required that diagnosis or symptoms. One sign of this was the relatively high proportion (66.7%) of individuals with probable post-COVID syndrome included in the study. This, together with the multitude of mental symptoms shown in people with post-COVID syndrome (20), highlights the need for psychological interventions that go beyond efforts aimed at addressing the somatic symptoms caused by COVID-19, even if this was not the primary target population of the present study. Another possible reason for the recruiting difficulties could be that there was less need for treatment for psychological symptoms related to the pandemic or its consequences, even though earlier studies have shown that virus outbreaks can still impact mental health after they end (84–87). Furthermore, the individuals in the present study had to answer multiple online questionnaires included in the pre-treatment measurement. Sixteen individuals began the measurement but did not complete it. At the same time, all questionnaires were administered based on the need to gather thorough information and assess whether the treatment format would be adequate for the person in question. Additionally, the number of questionnaires used in this study was similar to previous studies conducted by the same research group, in which more people applied [e.g., (42)].

The recruitment process and sample characteristics impacted our choice of design, result analyses, and possible interpretations of the results. Due to the low number of included participants (N = 24), we opted for a within-group design instead of randomizing the participants to a treatment group or a waitlist control group. As a result, it is more difficult to draw causal conclusions from the findings, since control over potential third-variable influences is reduced compared to when using an RCT design (88). However, the advantage of a within-group design in this study is that more participants could undergo the ICBT simultaneously, providing more information about the treatment's effectiveness at the end of the COVID-19 pandemic before it was declared over. Additionally, it can be argued that it is more ethically justifiable not to make half of the participants wait for intervention when they have applied to take part in the treatment for symptoms they are currently experiencing, even if the symptoms do not increase during that waiting time (89). The heterogeneity of the sample also influences the results and interpretation of these. There was a relatively wide range in age (20–67), employment status, and education level, which suggests that the sample is representative of the intended population, namely adults with psychological symptoms during the final phase of the COVID-19 pandemic. However, more than half (16 participants) were likely to meet the diagnostic criteria for post-COVID syndrome, while eight individuals were not assessed to meet the criteria. Of those answering the post-treatment measurement, and thus what data were used in the result analyses, two-thirds (10 of 15) of the individuals were assessed as probably having the post-COVID syndrome. Subsequently, the sample might consist of individuals from two somewhat different populations. Although no statistical tests were conducted regarding the symptom levels or changes in symptoms during the treatment, it could be hypothesized that individuals with and without post-COVID may have different needs in psychological treatment. At the same time, this may reflect individuals who experienced psychological symptoms during the final phase of the pandemic—with some with somatic and medical symptoms (90) and others without (1, 13)—even though the proportion of participants probably having post-COVID is higher in this study than in the general population. Moreover, in the present study, we were not able to definitively confirm or diagnose participants with post-COVID syndrome, which is why the term “probable” post-COVID is used. This limitation stems from the fact that we neither met participants in person nor had access to their medical records. Future studies should address this by including confirmed diagnoses when investigating differences between individuals with and without post-COVID syndrome.