Changes in Mental Health during the COVID-19 Pandemic among Representative Sample of Young Adults from Germany, Israel, Poland, and Slovenia: A Longitudinal Study.

The aim of this cross-national longitudinal study was to identify a change in mental health indicators: coronavirus-related post-traumatic stress disorder (PTSD), perceived stress, and fear of vaccination (FoVac). The first measurement (T1) took place in February 2021, and the second (T2) took place in May-June 2021. The sample consisted of 1723 participants across Germany, Israel, Poland, and Slovenia, between the age of 20 and 40 (M = 30.74, SD = 5.74). A paired-samples Student's t-test was used for testing the differences between T1 and T2. A repeated measures two-way ANOVA was performed to examine changes over time (T) and across the countries (C). A significant although small decrease at T2 was found for coronavirus-related PTSD, perceived stress, and FoVac. A significant main effect was found for T, C, and TxC for all variables, except the interaction effect for coronavirus-related PTSD and perceived stress. A medium effect size was found for coronavirus-related PTSD and FoVac across countries as well as perceived stress over time. A small effect size was revealed for coronavirus-related PTSD and FoVac over time, perceived stress across countries, and interaction for FoVac. A significant improvement in mental health was demonstrated across the four countries (particularly in Israel); however, there were still differences among each of them. Therefore, the cross-national context should be taken into consideration when analyzing the effects of the COVID-19 pandemic on mental health.