Introduction and Rapid Spread of SARS-CoV-2 Omicron Variant and Dynamics of BA.1 and BA.1.1 Sublineages, Finland, December 2021

Abstract

T he most recent SARS-CoV-2 variant of concern, Omicron (Pango lineage B.1.1.529), was first detected in South Africa (1), although it might have emerged elsewhere, and has since spread globally at an unforeseen speed. Notable examples include a superspreading event in Norway (2) and the rapid increase in incidence in Denmark (3) despite high vaccination coverage (83% of infected persons had received 2-3 vaccine doses). This rapid spread indicates the novel variant's exceptional transmissibility, as well as its potential for reinfection and vaccination breakthrough. We describe the genotypes of cases of Omicron entering Finland from their early spread up to established community transmission through the first week of January 2022. No ethics approval was needed because this study was based on routine CO-VID-19 surveillance data. The study regarding Helsinki University Hospital (HUH) samples was approved by the local ethical and research committee (Helsinki and Uusimaa Hospital District [HUS]; Clinical microbiology of COVID-19: diagnostics, laboratory findings and biorisks; HUS/244/2021). The StudyA total of 99,988 samples found positive for SARS-CoV-2 by reverse transcription PCR, 12.1% of 825,006 total samples tested, were detected in Finland during the study period, November 29, 2021-January 6, 2022 (Figure 1). Weekly positivity rates among persons tested rose from 6.1% of 156,077 in week 48 to 25.6% of 172,451 (3.1% of the Finnish population) in week 52 (https://sampo.thl.fi). In HUS, test positivity increased from 5.0% to 36.7% over the corresponding weeks 48-52. After a change in testing strategy favoring home antigen testing, the number of registered SARS-CoV-2 cases dropped (Appendix, https://wwwnc.cdc.gov/ EID/article/28/6/22-0515-App1.pdf).We estimated the proportions of Omicron variant lineages BA.1 and BA.1.1 within HUS by comparing PCR-based data on S-gene target failure (SGTF) to that of other circulating lineages (Figure 1; Appendix). The results showed a decrease in SGTF rates from week 24, when the proportion of the Alpha variant (B.1.1.7) was declining, to near 0 when the Delta variant (B.1.617.2) was dominant. This decrease aligns well with sequence-confirmed lineage turnover

Respiratory virus circulation in children after relaxation of COVID‐19 restrictions in fall 2021—A nationwide register study in Finland

“…Those remained dominant until June 2021, when the delta variant came to Finland from football tourists returning home from Russia and UEFA Euro 2020 13 . Delta remained as the main variant until December 2021, when omicron took the dominant role in 3 weeks 14 …”

“… 13 Delta remained as the main variant until December 2021, when omicron took the dominant role in 3 weeks. 14 …”

“…13 Delta remained as the main variant until December 2021, when omicron took the dominant role in 3 weeks. 14 Finland decided to renovate the test, tract, and isolate strategy in August 2021. First children aged under 12 did not require COVID-19 testing if symptoms were mild.…”

Emergence of New SARS-CoV2 Omicron Variants after the Change of Surveillance and Control Strategy

“…In fact, more than 100 sub-linages had been designed in May 2022 ( (accessed on 30 May 2021)). Because there is a geographic distribution of variants, local circulation data are as important as national level data [ 13 , 15 , 19 , 20 , 21 , 22 ].…”

Recapping the Features of SARS-CoV-2 and Its Main Variants: Status and Future Paths

“…In the preceding months to this review, a set of Omicron sublineages have been detected; BA.1 and BA.1.1 were the first to be reported and presented a rapid dissemination [ 138 ]. In a short period of time, two additional variants, BA.2 and BA.3, were also noticed.…”