Lockdown policies applied worldwide to limit the spread of COVID-19, and mainly based on health considerations, have negatively impacted on public transport (PT) usage, suspected as a means for the virus spreading due to difficulties ensuring social distancing. This resulted not only in a setback to sustainable mobility, but also impacting on equity and social exclusion issues. The paper aimed to cover this topic, investigating the conjecture that the spread of the coronavirus is directly correlated to PT usage. A correlation analysis among the daily number of certified coronavirus cases and the PT trips measured in the day in which the contagions occurred was performed within the second wave in Italy. The appropriateness of the case study is twofold because Italy was one of the main European countries with a high mass contagion and because the vaccination campaign had not yet started in Italy. Estimation results show a high correlation (up to 0.87) between COVID-19 contagion and PT trips performed 22 days before. This threshold indicates that quarantine measures, commonly set at two weeks and based only on incubation considerations, were inadequate as a containment strategy, and may have produced a possible slowdown in identifying new cases and hence, in adopting mitigation policies. A cause–effect test was also implemented, concluding that there is a strong causal link between COVID-19 and PT trips. The main issues discussed in this research cover the transportation and the health filed but also laid the groundwork for ethical considerations concerning the right to mobility and social equity. Obtained results could yield significant insights into the context variables that influence the spread of the virus, also helping appropriate definition of restrictive policies, thereby ensuring a sustainable recovery and development of urban areas in the post-pandemic era.