National Center of Infectious and Parasitic Diseases, Sofia, Bulgaria

Communication on the spread of SARS-CoV-2 variants in the country December 23, 2025

The NCIPD has successfully analyzed 62 clinical samples with SARS-CoV-2 using next-generation sequencing. The samples were collected from patients with COVID-19 across 13 regions of the country between October 7, 2025, and December 03, 2025, and were sent by 13 laboratories.

Omicron and its subvariants were detected in all samples tested. SARS-CoV-2 variants defined by WHO as Variants Under Monitoring (VUM) (as of November 28, 2025) were detected in 3 patient samples, N.B.1.8.1 in 2 (3.2%) samples and XFG in 1 (1.6%) sample, respectively. In addition, XFG subvariants (XFG.x 55/88.7%) as well as (4/6.5%) other SARS-CoV-2 subvariants were detected.

The Nextclade v3.8.2 program was used to define SARS-CoV-2 variants. An epidemiological analysis is underway.

For information on the classification of SARS-CoV-2 variants and sub-variants, please visit: https://cov-lineages.org/index.html

For an up-to-date classification of the variants of concern (VOIs), please visit:

https://www.ecdc.europa.eu/en/covid-19/variants-concern

https://www.who.int/en/activities/tracking-SARS-CoV-2-variants/