The COVID-19 pandemic had an impact on pupil’s daily lives worldwide, emphasising the pivotal importance of infectious diseases. This study aims to delineate the teaching of diseases in middle schools, investigating how content and instruction was influenced by the pandemic. Semi-structured individual interviews were conducted with teachers. The analytical method involved thematic analysis. The first analysis concerned teaching content and was based on the framework of contagion literacy. The second analysis investigated the teaching approaches and used an inductive analysis. Our findings suggest that the pandemic had an impact on the enacted biology teaching in relation to diseases. Teaching largely revolved around student-initiated, question-driven discussions about current events related to societal health initiatives within schools, rather than expanding the planned biology curriculum. The main finding is that teachers focused on hygiene and to influence students’ behaviours interactively, and that the pandemic was not fully exploited by the participating teachers to develop more curriculum-based teaching including functional and critical health literacy perspectives. The study recommends that biology teachers collaborate with school health teams and engage in interdisciplinary work. It also suggests amending primary science teacher education to meet the need to teach the young people in the event of future pandemics.