## 4 Discussion
The fact that B.1.177 was defined by the S:A222V mutation in the Spike protein could also confer a significant advantage to the virus infectivity, favouring its rapid selection and dissemination. B.1.177.60 was the first lineage to over-dominate others, and in September of 2020 this lineage was observed in Lithuania for the first time. There is no evidence of any appreciable effect of A222V on the phenotype of the virus (i.e., infectivity and transmissibility), and thus it is generally assumed that its increase in abundance was random rather than a selection advantage [25]. As we can see in Figure 3, this lineage is notable for very fast initial spread rate--it is next to AY.4.5 (Delta sub-lineage), and within a little more than one month and a half this lineage reached 50% of all month-wise sequenced cases. Throughout the propagation period, eight sublines were identified, of which the most spread-out was the Lithuanian subine B.1.177.60, which had appeared quickly after the emergence of B.1.177, which had its last cases in Lithuania observed on 21 st of November 2021. As we can see in Figure 4, this lineage spread to Lithuania is linked with Nordic countries (Denmark, Norway). Since the lineage was discovered, n = 5162 sequences were produced from sampled cases worldwide. The mutations present in this sub-lineages spike protein were S:L18F and ORF3a:V77F, in addition to the conventional B.1.177 mutations ORF1b-P314L, S:A222V,S:D614G, ORF8:S84L, ORF10:A220V, and ORF10:V30L. Although B.1.177 has been introduced to Lithuania many times, from the profile of hereditary mutations we can say that the vast majority of cases caused by the currently circulating B.1.177 lineage originated from several larger outbreaks. It is the first virus lineage of Lithuanian origin that is widely distributed abroad (mainly in Northern Europe), with the total percentage of cases being 57.0% in Lithuania, 14.0% in Latvia, 12.0% in Denmark, 6.0% in Finland, and 3.0% in Estonia [23]. Thus, the trend of local spread remained the same. In 2021, in February, the peak of this lineage was reached, and with the introduction of the first variant of concern (VOC) B.1.1.7, also known as Alpha, it began to advance this over-dominated lineage. B.1.1.7 (Alpha variant) was first identified in the United Kingdom in late 2020 and was temporally associated with an increase in regional infections, and the spread to Lithuania is also linked with the United Kingdom. This variant contains more than a dozen mutations when compared with other circulating lineages, having several of them within the spike protein. Subsequently, it became the predominant variant in many countries, until the emergence of the Delta variant. In Lithuania, since the first case of B.1.1.7, a very rapid spread has been observed, with the number of sequenced samples of B.1.1.7 doubling in amount every two week in Lithuania, while the Alpha variant was distinguishable based on the failure to amplify the S gene fragment (S-dropout), caused by S:H69-70 del [26] (Figure A2). Due to the delay of sequencing results and being aware of the new VOC, the Lithuanian government decided to take a \"snapshot\" of detecting B.1.1.7 distribution across the country by collecting and analysing all samples at a high priority rate. According to the results of the research, it was observed that, in Vilnius, Utena, and Marijampole counties, this variant accounted for 70% or more of new cases at that time, and in the other part of Lithuania its prevalence was at least 25% (Figure A3). According to the Lithuanian department of statistics, the regions of Lithuania where the B.1.1.7 virus lineage was predominating led in terms of both cases of illness and hospitalization in the country. At that time, infections with COVID-19 in Vilnius County accounted for 54% of all cases in Lithuania, and the number of cases diagnosed doubled since February. Thus, it is clear that this lineage has contributed significantly to the increase in the number of local infections.