Data collection and management
At enrolment, participants completed a questionnaire that included questions about demographics, comorbidities, previous SARS-CoV-2 infection and SARS-CoV-2 vaccination history. Study staff then contacted participants weekly, using a standard questionnaire, to ask participants if they had experienced any symptoms in the past week (fever, cough, general weakness, fatigue, headache, muscle ache, sore throat, runny nose, shortness of breath, lack of appetite, nausea, vomiting, diarrhoea, altered mental status, loss of taste, or loss of smell), and to ask about the details of any new COVID-19 vaccines participants had received.
We advised all participants who became symptomatic to attend testing facilities at the study hospitals, where trained nurses collected nasopharyngeal swabs, which were tested at on-site government-accredited laboratories or other Ministry of Health laboratories for SARS-CoV-2 by RT-PCR. Symptomatic participants completed an additional survey that included information about date of symptom onset, clinical care-seeking, and details of PCR testing and results. PCR-positive participants were interviewed again 30 days after their positive test, at which time further details about their course of illness, medical care, hospitalization, and complications were collected.
Data from interviewer-led questionnaires and laboratory records were entered and stored securely using the Sorgular.az platform (Azerbaijan Public Health Reform Center). Participants’ reports of positive PCR results were verified using the two national SARS-CoV-2 laboratory databases – the Etabib electronic medical records database, and the Ministry of Health (MoH)/Mandatory Health Insurance database – to which all SARS-CoV-2 PCR tests performed in public and private laboratories in the country are required to be reported. Participants’ COVID-19 vaccination history was verified using the national vaccine registry (Rendezvous, Azerbaijan Ministry of Health). Study staff contacted participants to resolve discrepancies between data from questionnaires and those from national databases, and to complete questions from study questionnaires that had not been answered.