Hacettepe Health Cohort: A Prospective Follow-up of the General Health Status and Effectiveness, Durability and Adverse Effects of COVID-19 Vaccine Among Students of Medical and Dental Schools

The study was planned, and ethical approval procedures were initiated in late January, 2021. However, serial official approval processes delayed the initiation of the study beyond the pre-planned initiation date (late in March 2021, to catch the 28th day after the second dose of CoronaVac vaccine). Thus, the study plan was revised, and so were the approval processes.

The planned prospective cohort study started its recruitment process in June, with the first enrollment on June 21, 2021. The study is an open cohort; vaccination times vary, some students participated in the first visit, but have/can leave the study before May 2023 (the planned closure time for testing); some students did not participate in the first visit (in June-July 2021), yet preferred to be involved in the study bythe time of the second visit (October 2021) and so.

Participants are being recruited from students of medical school (grades 4,5, and 6) and dental school (grade 4 and %), and are involved in the study for all/some of the procedures offered. The study aimed to:

1. Investigate the sociodemographic characteristics, health status, life habits, quality of life (via validated indices), COVID-19 status, vaccination status for SARS-CoV-2, use of non-pharmaceutical preventive measures against COVID-19. These will be accomplished through online, depersonalized, self-completed standardized questionnaire and use of validated scales.;
2. Complete anthropometric measures and physical examination at each visit;
3. Check blood levels for complete blood count, renal function tests, liver enzymes, D-dimer, vitamin D, HbA1c levels, and lipid profile;
4. Check vaccine-induced immunity using quantitative, Anti-SARS-CoV-2 Receptor Binding Domain kit (Abbott Laboratories) at enrolment and each subsequent visits;
5. Evaluate the durability of vaccine-induced immunity, as measured by antibody levels periodically (at 3rd, 6th, 12th and 24th month after full immunization following full vaccination, i.e. 2 doses plus 28 days);
6. The cohort will be followed up to 24 months (through September 2023) for detecting COVID-19 infection and/or related hospitalization, intensive care unit (ICU)-admission or death; also, to study the potential association with personal risk factors and/or vaccine-induced immunity;
7. A nested, test-negative case-control study is integrated into the the cohort, such that each time a new COVID-19 case is identified (with a PCR-positivity), two gender and school/grade matched controls will be invited for PCR testing. Blood will be drawn from PCR test negative controls at the day (or within 1 day later) of the PCR-positivity of the case detected. This nested case-(test-negative) control design will enable to study the association between infection and current Anti-Spike1 RBD antibody levels, controlling for personal risk factors;
8. Given the considerable amount of asymptomatic infections among vaccinated individuals, 150 participants will be selected from among volunteers for 6 consecutive PCR-testing, with 15 days intervals between each testing.

Three study designs will be used to reach study objectives; namely, a large prospective cohort (for evaluating changes in general health status and neutralizing antibody levels, as measured by SARS-CoV-2-RBD Abs); a subcohort for periodical PCR testing to detect asymptomatic infection rates;