שאלה משלב א׳ בבריאות הציבור · מועד 2024 (Sep), שאלה 97

Correct: B — a prospective cohort study. The investigators recruited two groups defined by their vaccination status, then followed them forward in time for 70 days, actively inviting them to the clinic and performing PCR tests during the follow-up. The decisive features are that the exposure was not allocated by the investigators, which excludes a trial, and that the follow-up and the outcome ascertainment occurred after the study began, which makes it prospective rather than historical, and allows the active, uniform outcome ascertainment that avoids the detection bias to which passive follow-up would be prone.