Title : A strong dominance in the spread of influenza viruses over that of the SARS-CoV-2 during the 2022/2023 season in Bulgaria
After a period of two seasons of absence (2020/2021) or low prevalence (2021/2022) of influenza viruses, the 2022-2023 season was characterized by high influenza activity in Bulgaria. The objectives of this study were to analyze the pattern of influenza virus circulation with respect to that of SARS-CoV-2 during the 2022-2023 season. Influenza type A/B viruses and SARS-CoV-2 were tested simultaneously using a Multiplex real-time RT-PCR kit (FluSC2, USA). The spread of influenza viruses began earlier – in mid-November 2022 and peaked in the 3rd week of January 2023 amid a low spread of the SARS-CoV-2. Seasonal influenza viruses A(H1N1)pdm09, A(H3N2), and B/Victorialineage were detected in 256 (13.4%), 189 (9.9%), and 22 (1.2%) out of 1913 patient samples studied, respectively, and SARS-CoV-2 was identified in 78 (4.1%) samples. Six cases of co-infections between the influenza virus and SARS-CoV-2 were identified. The proportions of influenza detection in outpatients and inpatients were similar (25.7% and 23.2%, respectively). In SARS-CoV-2-infected patients, these proportions were 4.2% and 4%, respectively. Influenza viruses were detected in 6,5% (11/168), 21.6% (69/319), and 22.2% (8/36) of the studied patients with bronchitis/bronchiolitis, pneumonia, and CNS involvement, respectively. SARS-CoV-2 was identified in 2.5% of patients with pneumonia. Clinical features of the infections were analyzed. In conclusion, a strong dominance in the spread of influenza viruses over that of the SARS-CoV-2 was found during the 2022/2023 season in Bulgaria, which is related to the dropping of non-pharmaceutical antiCOVID-19 measures and low coverage with influenza vaccine in the country. Influenza A viruses predominated with a larger proportion of A(H1N1)pdm09 viruses. This work is supported by: contracts KΠ-06-H 43/5/30.11.2020/ and Grant BG05M2OP001-1.002-0001-C04
Audience take away:
nfluenza has great clinical and epidemiological significance. Influenza viruses affect millions of people worldwide. There are 600 million cases of influenza worldwide each year, with 3 million having severe disease. Awareness of the prevalence of influenza and its clinical significance is an important part of our health and disease education. The threat of new influenza pandemics is a hot topic today, and therefore there is a need to track the spread of influenza viruses and facilitate the development of seasonal vaccines that would help reduce hospital admissions worldwide. Such information is important for developing optimal strategies for influenza prevention and control. The results of this study confirm the diversity of circulating influenza viruses and the presence of co-infections with SARS-CoV-2, which would pose a risk of worsening patients' conditions. The emergence of such co-infections at a higher rate since the beginning of the pandemic indicates the need to develop vaccines that include both pathogens.