There have been conflicting views on whether helminth infections modulate disease outcomes during SARS-CoV-2 infection. In this study, Oyesola et al. infected K18-hACE2 mice (which express human ACE2 and are therefore susceptible to SARS-CoV-2) with the lung-migrating helminth Nippostrongylus brasiliensis, waited for the mice to clear the infection, and then infected the mice intranasally with SARS-CoV-2. Mice previously infected with N. brasiliensis showed decreased mortality in response to SARS-CoV-2 infection (60% survived compared with 20% of controls). By contrast, previous infection of mice with an intestine-restricted helminth did not confer a survival benefit. Further experiments suggested that the protective effect was dependent on Arginase 1+ monocyte-derived alveolar macrophages that replace the resident alveolar macrophages during N. brasiliensis infection. These N. brasiliensis-induced macrophages enhanced the recruitment and activation of virus-specific CD8+ T cells during subsequent SARS-CoV-2 infection, which limited disease severity. Therefore, previous exposure to lung-migrating helminths may promote immunity to SARS-CoV-2 by remodelling pulmonary macrophage populations. Interestingly, lower levels of COVID-19 mortality and morbidity have been reported in regions where helminth infections are prevalent.