Vaccines | Free Full-Text | The Fear of SARS-CoV-2 Infection versus the Perception of COVID-19 Vaccination amongst Older Adults in Urban Areas (CoV-VAC-PL Study): A Polish Community-Based Study

2.1. Participants and Study Design

The study sample encompassed a population of 800 individuals aged 60 years and older randomly picked up from a representative sample of all the residents in 16 voivodeship cities (50 individuals from each of the following cities: Białystok, Bydgoszcz, Gdańsk, Katowice, Kielce, Kraków, Lublin, Łódź, Olsztyn, Opole, Poznań, Rzeszów, Szczecin, Warszawa, Wrocław, and Zielona Góra). Random sampling was based on names from and conducted through the PESEL (Polish acronym for Universal Electronic System for Registration of the Population) Register (Ministry of Digital Affairs, Warszawa, Poland). Respective individuals were selected by means of stratified random sampling in reference to sex and age. In the course of sampling, the ultimate study efficacy was taken into account. The expected study response rate stood at RR = 25%. That made it necessary to select 3200 respondents from the cities under consideration. The following subgroups were sampled: 34 females and 34 males aged 60–69 years, 33 females and 33 males aged 70–79 years, and 33 females and 33 males aged 80 years and older (200 individuals in total) in each of the said cities.

This study was conducted by interviewers who were 2nd degree students in nursing programmes (enjoying the right to practise the nursing profession), who had been selected through the competition procedure, in the aforementioned cities during the period from 1 March to 30 November 2023. The questionnaire was implemented into the dedicated mobile application MUBSurvey 1.0 (Nfinity Sp. z o.o., Wrocław, Poland) that had been developed for the purpose of this study. Each of the interviewers obtained a login and password for their own individual user account set up by the study team, upon having installed the application on his or her own mobile device. Before the study commenced, all the interviewers had to be trained online by the study team to the extent of the application operational manual and the substance-based knowledge indispensable to acting as the interviewer; the training covered not only the instructions for filling out the questionnaire but also a practical tutorial making use of the study response scales.

Completing an informed consent form to take part in this study and a lack of cognitive disorders constituted the study inclusion criteria. The Mini Mental State Examination was performed for the purpose of screening the individuals under study in order to exclude cognitive disorders. The individuals who had scored below 27 points were ultimately excluded from the study. This gave rise to the exclusion of 17 people from the total number of 1190 individuals (1.43%). Furthermore, any respondent could withdraw at any stage of the study. Thirteen withdrawals from the study were recorded throughout the course of its duration (out of the total number of 1190 individuals), which accounted for 1.1%.

The field study was conducted in the form of personal meetings with the randomly selected respondents. It was also fully anonymised; personal particulars obtained from the Ministry of Digital Affairs, which the interviewers had been provided with, were used exclusively for organising the field study efficiently and reliably, and they were not included in the data obtained through the study. A single, full interview per one respondent took approximately 15 min on average. Should a respondent have been unable to be found and the interviewer did not receive any information on her or his whereabouts (a respondent’s death, hospitalisation, change in residence address, another reason), two subsequent attempts were made at the designated address. A respondent’s refusal to take part in the study entailed filling a reason for that in the questionnaire. In total, 360 refusals to take part in the study out of 1190 visits paid to respondents (30.25%) were recorded.

The field study conducted by the interviewers was continually supervised by the study team. In order for the interviewer to save a complete questionnaire in the application, a text message code had to be keyed in that had been received by the interviewer onto a mobile phone number previously provided. In the case of people who did not have a mobile phone, an automatic message containing a numeric code was forwarded as a voice message to the landline phone number previously provided.