Introduction: The first two years of the SARS-CoV-2 pandemic were marked by an unprecedented impact on the survival of the kidney transplant patient worldwide, a population that accumulates risk factors for worse outcomes and has reduced vaccine response. However, from the end of 2021, the pandemic acquired new nuances, with the broad availability of booster doses of the vaccine – in Brazil, since 08/26/2021 – and the emergence of the Omicron variant, more infectious but possibly less lethal. The aim of our study was to describe how the new era of the pandemic differed from the previous one in a large cohort of renal transplant patients being followed up at a single center.

Methods: This single-center prospective cohort study included kidney transplant recipients with confirmed COVID-19 between 03/20/2020 and 02/15/2022. The outcomes of interest were incidence of confirmed SARS-CoV-2 infection, need for hospitalization, mechanical ventilation, dialysis and COVID-19 associated death within 28 days from the onset of symptoms. For the present analysis, we arbitrarily separated the patients into two eras, named "Era 1" (03/20/2020 to 12/02/2021) and "Era 2" (12/17/2021 to 02/15/2022), considering the emergence of the Omicron variant in Brazil at the end of the year 2021 and that there were no cases registered between 12/02/2021 and 12/17/2021. Genetic sequencing to identify the variants was not available in the center.

Results: Among the 10,497 kidney transplant recipients in follow up, there were 3,327 cases of confirmed COVID-19 in the entire observation period. There was an increase in the incidence rate from 0.3 cases/1000patients-day in Era 1 to 1.72 cases/1000patients-day in Era 2, and the sharp increase in the number of cases in the last Era is demonstrated in Figure 1. There was no difference in the median age (51 [IQR 42-60] years versus 50 [IQR 40-61] years, p=0.447) or in the proportion of male patients (60.4% versus 58.5%, p=0.294) between the two Eras. There was a significant decrease in the rate of hospitalization (57.5%% versus 29.2%, p<0.0001), need for mechanical ventilation (29.9% versus 16.3%, p<0.0001), dialysis (25.6%% versus 9.1%, p<0.0001) and COVID-19 related death (26.9% versus 10%, p<0.0001, as demonstrated in Figure 1).

Conclusion: There was a clear change in the dynamics of the pandemic from December 2021 among renal transplant patients, with higher incidence and lower severity of COVID-19, possibly due, but not limited to, booster vaccination and lower pathogenicity of the Omicron variant.