The COVID–19 pandemic had an immense impact on societies globally, emphasising the pivotal importance of understanding infectious diseases. This study was conducted to delineate the possible influence of the pandemic, by comparing how infectious diseases are portrayed in biology textbooks (school years 4–6 and 7–9) published before and after the COVID–19 pandemic outbreak. Data was subjected to content and thematic analysis, employing contagion literacy as an analytical framework. The contagion literacy framework identifies six content themes important to teach: contagions, transmission routes, hygiene, vaccinations, antibiotics and antibiotic resistance and sexually transmitted diseases that can be divided into three health literacy levels; functional, which focuses on factual knowledge, interactive, an invitation to what one should do and critical, which requires a higher awareness with critical reflection. The main conclusion from the comparative analysis was that very few changes were made in the textbooks as a consequence of the pandemic and an overall dominance of functional health literacy. However, critical health literacy descriptions of vaccinations increased in the aftermath of COVID–19 in lower secondary textbooks (7–9), while simultaneously content descriptions about antibiotic and antibiotic resistance were reduced. Critical health literacy aspects of vaccination were included in biology textbooks published only after the pandemic. Concomitantly, the inclusion of descriptions of linkage between contagions and infectious diseases and incubation periods was also found in textbooks published after the pandemic. Implications for curriculum development and the impact on teaching and learning are discussed.