This study has several limitations. First, since this is not a cohort study, we could not assess whether the COVID-19 pandemic led to the development of mental disorders in individuals with no history of mental disorders. In addition, the baseline data collection was conducted in November 2017, which is about two and half year before the COVID-19 data collection, and this might increase a chance of confounding. Second, due to the extraordinary epidemiological situation caused by the COVID-19 pandemic, we were not able to collect data by means of a face-to-face interviewing, instead relying on CAWI and CATI methods. The use of these methods may have introduced selection bias as some demographics (i.e. individuals without phone and/or internet access) could not participate. Third, while assessing a presence of GAD, the psycho-diagnostic tool M.I.N.I. asks the following question: ‘Is the patient's anxiety restricted exclusively to, or better explained by, any disorder prior to this point?’ This question is intended for clinicians, and it makes sense when all of the modules of MINI are used, which was not the case in 2020. Hence, we relaxed this criterion, and this has led to a relatively high prevalence of GAD in both of our samples. Fourth, since the data were collected after the strictest lockdown measures had loosened, the full extent of COVID-related mental health problems may not be represented. Consequently, it is likely that at the peak of the pandemic and associated lockdown, mental health symptoms were even higher. In China, this was found in a study reporting the progression of mental health symptoms at multiple points over COVID-19, showing that the highest levels of mental health problems presented during the peak of virus spread and associated lockdowns (Wang et al., 2020a, 2020b). However, the study benefits from a considerably large number of participants, obtained using rigorous sampling, representative of the Czech adult general population. Second, we were able to compare our results to a baseline dataset collected prior to COVID-19, which measured the prevalence of mental illness using the same instrument on a similar population. Third, data collection for this study was finalised prior to the lifting of the most severe restrictions imposed by the government in response to COVID-19. Thus, the results of the study should be interpreted with existing contextual confounders within the Czech context, but are likely not biased by a return to society with new norms and regulations surrounding distancing and functioning.