Epidemiological Characterization of Patients in the First Eight Weeks Following Detection of SARS-CoV-2 B.1.1.529 (omicron) Variant in Cuba.

Introduction: In November 2021, omicron-a new SARS-CoV-2 variant-was identified in South Africa and almost immediately, WHO declared it a 'variant of concern'. In view of its rapid worldwide spread and its imminent introduction in Cuba, genomic surveillance was strengthened.

Objective: Describe cases during the first eight epidemiological weeks (epiweeks) of SARS-CoV-2 infection attributable to omicron variant in Cuba by clinical and epidemiological variables.

Methods: From epiweek 48, 2021 to epiweek 4, 2022, 288 nasopharyngeal swabs were processed for sequencing of a 1836 bp fragment of the S gene. Variants were identified according to GISAID database and confirmed by phylogenetic analysis. Variants' association with clinical and epidemiological outcomes was assessed.

Results: The first cases of omicron variant were imported, mostly from African countries and the United States. During the period studied, omicron was detected in 83.0% (239/288) of cases processed, while the delta variant was found in 17.0% (49/288). Most persons infected with omicron were symptomatic (63.2%; 151/239) and fully vaccinated (65.3%; 156/239); severe cases and deaths occurred mainly among patients aged ≥65 years (92.9%; 13/14), and 12 of these deaths occurred in fully vaccinated persons (92.3%; 12/13). Omicron spread rapidly throughout the country (from 10% of cases in epiweek 48, 2021, to 100% by epiweek 4, 2022), displacing the formerly predominant delta variant.

Conclusions: Omicron's rapid expansion in Cuba was associated with increased incidence but not with a higher case fatality rate. The relatively milder disease in those infected with this variant could be influenced by the high vaccination coverage, along with the natural immunity acquired as a consequence of previous virus infection.