Coronavirus disease 2019 infection severity among different variants in children under 2-years old in Brazil.

To analyze whether there is a significant difference in the virulence, symptoms, and outcomes of different Coronavirus Disease 2019 (COVID-19) variants in children under 2-years of age. We collected data from the Sistema de Informação de Vigilância Epidemiológica da Gripe, a nationwide Brazilian database on severe acute respiratory syndrome. The patients were classified according to four variants of concern: wild-type, gamma, delta, and omicron. The wild-type variant was defined as the baseline. A total of 11,153 patients were analyzed. The risk of presenting dyspnea (adjusted Odds Ratio[Aor = 1.20], 95 % Confidence Interval [95 % CI 1.07-1.34]) was higher in patients with gamma infection. Respiratory discomfort was more likely to be present for the omicron (Aor = 1.29, 95 % CI 1.15-1.43) and gamma (aOR = 1.26, 95 % CI 1.13-1.41) infections. Desaturation was more likely to be present for the omicron (aOR = 1.67, 95 % CI 1.50-1.86), gamma (aOR = 1.16, 95 % CI 1.43-1.79), and delta (aOR 1.41, CI 95 % 1.18-1.68) infections. Infection by the omicron variant was a protective factor for intubation (aOR = 0.78, 95 % CI 0.67-0.91) and death (aOR = 0.43, 95 % CI 0.35-0.53). Additionally, delta infection was a protective factor against death (aOR = 0.60, 95 % CI 0.43-0.85). The wild-type variant was responsible for most of the cases that evolved with death. Omicron appears to be responsible for milder symptoms than delta. Children between 1 and 6 months of age account for most cases, which is a concern because there is no vaccination coverage.