SARS-CoV-2 Omicron Variant in Croatia—Rapid Detection of the First Case and Cross-Border Spread

Abstract

Background: Due to rapid spread, the Omicron variant has become the dominant SARS-CoV-2 variant responsible for infections worldwide. We present the first detection of the Omicron variant in Croatia which resulted in rapid cross-border spreading. Methods: Whole-genome sequencing was performed using the Illumina MiniSeq sequencing system. SARS-CoV-2 lineages were identified using the PANGOLIN and GISAID databases. Results: The first case of the Omicron variant (BA.1.17) emerged in Croatia after a workshop held in Zagreb in November 2021. The patient reported a history of previous COVID-19 and received two doses of an mRNA vaccine. Three additional cases were detected among Croatian participants of the workshop. At the beginning of December, SARS-CoV-2 infection was confirmed in one participant from Montenegro and her husband. Phylogenetic analysis showed that the detected Omicron variants were closely related to the first Croatian case, confirming the connection with the workshop outbreak and rapid cross-border spreading. Subsequent analyses of SARS-CoV-2 positive samples in Croatia showed the rapid introduction of the Omicron variant and depletion of the Delta variant resulting in the fifth pandemic wave. Conclusions: Genomic monitoring and early detection of novel SARS-CoV-2 variants are essential to implement timely epidemiological interventions and reduce further transmission in the population.

How Different Predominant SARS-CoV-2 Variants of Concern Affected Clinical Patterns and Performances of Infected Professional Players during Two Soccer Seasons: An Observational Study from Split, Croatia

“…The sudden spread of COVID-19 among the club's players and the large number of infected players, six of whom were reinfected, raised the suspicion of Omicron VOC circulation, dominant at that time in Europe. At the time of the fourth cluster observed in season 2 in December 2021/January 2022, Omicron rapidly replaced the Delta variant as the dominant variant, and by week 2 of 2022 Delta constituted less than 15% of all Croatian positive samples [22]. A sharp increase in the number of cases was observed during Omicron dominance, because this variant evades the existing immunity and is inherently more transmissible than previous variants [22].…”

“…Since 9 February 2021, Croatia has monitored novel or emerging viral variants by whole-genome sequencing according to the ECDC protocol [21]. Representative and targeted positive samples have been sequenced weekly and the predominant virus variants in circulation in Croatia have been documented, with the data broken down by county [22,23].…”

Neutralizing Activity of SARS-CoV-2 Antibodies in Patients with COVID-19 and Vaccinated Individuals

“…Beta and Gamma variants were documented in a small number of samples. The first case of the Omicron variant was detected in November 2021 and spread rapidly, causing the fifth epidemic wave [ 26 , 27 , 28 ].…”