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.