SARS-CoV-2 infection outcomes associated with the Delta variant: A prospective cohort study

It is well established that fully vaccinated (≥2 doses) individuals may develop COVID-19. However, little is known about the specific prevalence of post-COVID-19 conditions associated with the Delta variant or the effect of vaccination on post-acute outcomes of COVID-19. In addition, how Delta variant infection severity compares in fully vaccinated individuals versus in those unvaccinated is unknown.

This prospective single-centre observational cohort study assessed adults with SARS-CoV-2 proven infection from August 1 to November 1, 2021. Study participants were enrolled in the Biobanque Québécoise de la COVID-19. Data on demographics, comorbidities, and severity of COVID-19 were collected. Simple and multiple logistic regressions were used to identify risk factors for post-COVID-19 conditions.

Among the 395 individuals who were interviewed by phone, 138 (39.4%) agreed to participate. Of the 138 participants, 62.8% were Delta-associated breakthrough infections that occurred in fully vaccinated individuals and 37.1% in unvaccinated individuals. The majority (93.5%) had a history of mild COVID-19 illness. The prevalence of Delta-variant-associated post-COVID-19 conditions was similar in both vaccinated (61.4%) and unvaccinated (51.4%) groups (p = 0.347). The number of symptoms during acute infection was an independent risk factor for post-COVID-19 conditions.

This study is the first to describe the incidence of Delta-associated post-COVID-19 condition. In this study, COVID-19 vaccination was not associated with decreased post-COVID-19 conditions in patients with breakthrough Delta infection. These findings have important implications for provincial services planning and underscore the need to develop alternative strategies to prevent post-COVID-19 conditions.