## 2 Materials and Methods
### Sampling and Survey Instrument  
An anonymous and structured questionnaire was developed based on previous similar studies [9; 10; 11; 12; 13] as well as on the World Health Organization (WHO) COVID-19 prevention and control measures [14]. A pilot survey was performed on a sample of 20 students prior to the main study to assess the relevance and understandability of the questionnaire. Minor revisions were made afterward. The online survey was sent via institutional email. We hypothesized that the academic major could have an effect on the students' knowledge, risk perceptions and adherence to NPIs, so we conducted a stratified sampling. Hence, we used a random number generator to select a sample of 25 males and 25 females from a sampling frame that included students attending all the university's majors (N. 28). The inclusion criteria required the participants to be undergraduate university students and to have voluntarily participated. The exclusion criteria included being under 18 and over 29 years of age.  
Potential participants were informed at the beginning of the questionnaire on the purposes of the study, on its voluntary nature together with the condition that they could terminate their participation at any stage of the survey. No compensation, course credit or other incentives were offered to the student for their time spent. The questionnaire could only be submitted once for each electronic device in an effort to reduce potential repeat responses.  
Participants were asked to respond to four questions relating to their socio-demographic characteristics (age, gender, marital status, academic major). Knowledge about routes of transmission and measures against the spread of COVID-19 were tested with six statements, rated on a 5-point Likert scale from strongly disagree to strongly agree. An overall knowledge score was calculated by assigning one point for each correct response and summing the scores for each statement (range 0-6). The overall median knowledge score of the respondents was then estimated and a total score of <50 th percentile was interpreted as poor knowledge,whereas a score of \(\geq\)50 th percentile as good knowledge. We assessed the perceived risk of COVID-19 according to three measured indicators on a 0-10 scale. The first indicator was an assessment of own personal risk of getting infected/getting infected again in case the respondent had already been ill from COVID-19 (vulnerability). The second indicator was an assessment of fear of falling ill with COVID-19. The third indicator corresponded to the expected prevalence of COVID-19 in the community. Adherence to preventive and control measures for COVID-19 (i.e., use of face mask; respiratory etiquette, such as covering mouth and nose with a flexed elbow when sneezing or coughing if they do not have a tissue; hand hygiene) were investigated by five questions on a 5-point Likert scale ranging from \"never\" to \"always\". The last section (two items, closed-ended with multiple answers and open option) explored the main sources of information adopted to inquire about news regarding COVID-19 and if the students needed further information about it. Validity was investigated in terms of content validity and factorial validity. The content validity of the items was established by a panel of experts including one epidemiologist, one public health professional, one infectious disease specialist and one social and behavioral sciences consultant.  
Ethical approval was granted by the Regional Human Research Ethics Committee (ID No. 101/2021/03/18). The research protocol did not encompass the collection of privacy-sensitive identity information data.