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The aim of this study was to investigate and obtain insights into the appearance, spread and impact of the Omicron variants and their sub-lineages in Cyprus by analyzing 611 high-coverage full-genome sequences for the period from November 2021 until April 2022. All viruses sequenced were identified to belong to either Delta (B.1.617.2) or Omicron (lineage BA.1 and BA.2, respectively), with a variety of different sub-lineages. A detailed analysis of the mutational profile is presented and discussed. The Omicron variant BA.1 was shortly followed by BA.2; despite emerging against a background of high vaccination (81% of adult population) and pre-existing natural immunity, they gave rise to the largest waves of infection, with daily numbers rising dramatically, highlighting their increased ability for immune evasion. Within a period of only five months, the percentage of the Cypriot population with a confirmed infection increased from ~15% of the total population to >57%. Despite unprecedented case numbers, a significant reduction in hospital burden and mortality was observed. Our findings highlight the role of the importation of new variants through travel and demonstrate the importance of genomic surveillance in determining viral genetic diversity and the timely identification of new variants for guiding public health intervention measures.

There is an ongoing effort to report data on SARS-CoV-2 antibodies in different individuals. Ninety-seven healthcare workers were enrolled in this study (Pfizer's BNT162b2, n = 52; and AstraZeneca's ChAdOx1-S, n = 45) and S1RBD-specific IgG antibodies were analyzed over time. Both vaccines induced S1RBD-specific antibodies after the second dose. A significant increase in S1RBD-specific IgG median levels 3 weeks following the second dose was detected (BNT162b2, 118.0 BAU/mL to 2018.0 BAU/mL; ChAdOx1-S, 38.1 BAU/mL to 182.1 BAU/mL). At 3 months post the second dose, a significant decrease in S1RBD-specific IgG median levels was also evident (BNT162b2, 415.6 BAU/mL, ChAdOx1-S, 84.7 BAU/mL). The elimination rate of these antibodies was faster in BNT162b2- rather than ChAdOx1-S- vaccinated individuals. A booster dose induced a significant increase in the S1RBD-specific IgG median levels (BNT162b2, 1823.0 BAU/mL; ChAdOx1-S, 656.8 BAU/mL). This study is the first of its kind to characterize S1RBD-specific IgG antibody responses in vaccinated healthcare workers in Cyprus. While the positivity for S1RBD-specific antibodies was maintained 3 months after the second vaccine dose, the level of these antibodies waned over the same period, indicating the importance of a booster vaccination. The results herein could complement the public health policies regarding the immunization schedule for COVID-19.