While several cross-sectional studies have suggested high burnout levels among health-care workers (HCW) during the Covid-19 pandemic, fewer studies have examined longitudinal trajectories of burnout. Objectives To examine (1) trajectories of change in levels of burnout among Norwegian HCW during a one-year period in the mid-phase of the Covid-19 pandemic (second, third, and fourth incidence rate peaks), and (2) how demographic and occupational variables, and pandemic-related experiences (e.g., own infection, severe infection in family, friend, or colleague, caring for deceased patient with Covid-19) were associated with such change. Methods Burnout was measured by the Copenhagen Burnout Inventory. Latent growth curve modeling was used to estimate trajectories of burnout symptoms, and predictors of starting point and rate of change in burnout levels. Results Starting points of burnout scores were, on average, low-to-moderate. Women, younger HCW, those living alone, and nurses had higher initial scores. Overall, burnout scores remained mostly unchanged across the study period. However, lower burnout scores at the initial assessment were associated with increasing scores over time. Being exposed to patients with Covid-19 and having a Covid-19 infection were associated with increased burnout over time. Conclusions While burnout symptoms among frontline health workers remained stable across the peaks of the Covid-19 pandemic overall, the study identified higher risk of worsening symptoms over time among certain demographic (younger personnel, females, and nurses) and highly exposed individuals and groups. These findings may be helpful for identifying frontline workers at particular risk of burnout during future public health emergencies.