NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION

week 50 of 2025 (08.12.25 - 14.12.25)

Summary

Influenza and ARI incidence data. Influenza and other ARI activity in Russia increased in comparison with previous week. The nationwide ILI and ARI morbidity level (106.2 per 10 000 of population) was higher than national baseline (82.9) by 28.1%.

Etiology of ILI & ARI. Among 11722 patients investigation 1823 (15,6%) respiratory samples were positive for influenza, including 235 cases of unsubtyped influenza A in 10 cities, 18 cases of influenza A(H1N1)pdm09 in 7 cities, 1562 cases of influenza A(H3N2) in 43 cities and 8 cases of influenza B in 6 cities.

49 influenza viruses were isolated on MDCK cell culture, including 48 cases of influenza A(H3N2) in Vladivostok (5), Moscow (6), Yekaterinburg (6), Kaliningrad (1), Novosibirsk (18), Saint-Petersburg (11), Yaroslavl (1) and 1 case of influenza B in Vladivostok. Since the beginning of the season 136 influenza viruses, including: 135 A(H3N2) viruses and 1 influenza B virus.

Antigenic characterization. Since the beginning of the season 2025-2026 28 influenza have been antigenically characterized by the NICs in Saint-Petersburg and Moscow, including: 1 influenza A(H1N1)pdm09 virus and 27 influenza A(H3N2) viruses. Virus A(H1N1)pdm09 was similar to the reference strain A/Victoria/4897/22 recommended in the vaccines for the Northern Hemisphere countries for the 2025-2026 season. 1 influenza A(H3N2) viruses was similar to the reference strain A/Croatia/10136RV/23, also recommended in vaccines for countries in the Northern Hemisphere for the 2025-2026 season, 14 A(H3N2) viruses were its drift variant, 11 viruses A(H3N2) were similar to  the reference strain A/Thailand/8/2022, 1 strain was a drift variant of the reference strain A/Thailand/8/2022.

Genetic characterization. Since the beginning of the season 2025-2026 sequenced 264 influenza viruses in Saint-Petersburg. 257 influenza A(H3N2) viruses were similar to the vaccine strain A/Croatia/10136RV/2023, of which 245 viruses belong to clade 3C.2a1b.2a.2a.3a.1 subclade K, 12 viruses belong to clade 3C.2a1b.2a.2a.3a.1. 6 A(H1N1)pdm09 viruses were similar to the vaccine strain A/Victoria/4897/2022 and were classified as clade 6B.1A.5a.2a.1, one strain was related to the reference strain A/Sydney/5/2021 and assigned to clade 6B.1A.5a.2a.

ARVI detections. The overall proportion of respiratory samples tested positive for other ARVI (PIV, ADV, RSV, RhV, CoV, MPV, BoV) was estimated in total as 11.8% (PCR).

In sentinel surveillance system clinical samples from 31 SARI patients were investigated by rRT-PCR for influenza, among them 13 (41.9%) cases of influenza A(H3N2) were recognized. 3 (9.7%) of 31 SARI patients were positive for coronavirus SARS-CoV-2. Among 31 SARI samples 7 (22.6%) cases positive for ARVI were detected including: 1 case of PIV, 4 cases of CoV and 2 cases of BoV infection.

Among from 17 ILI/ARI patients were investigated for influenza, among them 4 (23.5%) cases of influenza A(H3N2) were recognized. Among 17 ILI/ARI samples 4 (23.5%) cases positive for ARVI were detected including: 1 case of PIV, 1 case of ADV, 1 case of RhV and 1 case of CoV infection. Among 17 ILI/ARI samples no positive cases of coronavirus SARS-CoV-2 were recognized.COVID-19. According to the data obtained by NIC in Saint-Petersburg totally 14019 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 was detected in 530 (3.8%) cases.

Influenza and ARI morbidity data

Epidemiological data showed increased of influenza and other ARI activity in Russia in comparison with previous week. The nationwide ILI and ARI morbidity level (106.2 per 10 000 of population) was higher than national baseline (82.9) by 28.1%.

Incidence rate of clinically diagnosed influenza increased comparing to previous week and amounted to 3.36 per 10 000 of population, it was higher than pre-epidemic MEM baseline (0.45).

Hospitalization rate of clinically diagnosed influenza increased comparing to previous week and amounted to 0.72 per 10 000 of population, it was higher than pre-epidemic MEM baseline (0.099).

Influenza and ARVI laboratory testing results

Cumulative results of influenza laboratory diagnosis by rRT-PCR were submitted by 45 RBLs and two WHO NICs. According to these data as a result of 11722 patients investigation 1823 (15,6%) respiratory samples were positive for influenza, including 235 cases of unsubtyped influenza A in 10 cities, 18 cases of influenza A(H1N1)pdm09 in 7 cities, 1562 cases of influenza A(H3N2) in 43 cities and 8 cases of influenza B in 6 cities.

49 influenza viruses were isolated on MDCK cell culture, including 48 cases of influenza A(H3N2) in Vladivostok (5), Moscow (6), Yekaterinburg (6), Kaliningrad (1), Novosibirsk (18), Saint-Petersburg (11), Yaroslavl (1) and 1 case of influenza B in Vladivostok. Since the beginning of the season 136 influenza viruses, including: 135 A(H3N2) viruses and 1 influenza B virus.Antigenic characterization. Since the beginning of the season 2025-2026 28 influenza have been antigenically characterized by the NICs in Saint-Petersburg and Moscow, including: 1 influenza A(H1N1)pdm09 virus and 27 influenza A(H3N2) viruses. Virus A(H1N1)pdm09 was similar to the reference strain A/Victoria/4897/22 recommended in the vaccines for the Northern Hemisphere countries for the 2025-2026 season. 1 influenza A(H3N2) viruses was similar to the reference strain A/Croatia/10136RV/23, also recommended in vaccines for countries in the Northern Hemisphere for the 2025-2026 season, 14 A(H3N2) viruses were its drift variant, 11 viruses A(H3N2) were similar to the reference strain A/Thailand/8/2022, 1 strain was a drift variant of the reference strain A/Thailand/8/2022.

Genetic characterization. Since the beginning of the season 2025-2026 sequenced 264 influenza viruses in Saint-Petersburg. 257 influenza A(H3N2) viruses were similar to the vaccine strain A/Croatia/10136RV/2023, of which 245 viruses belong to clade 3C.2a1b.2a.2a.3a.1 subclade K, 12 viruses belong to clade 3C.2a1b.2a.2a.3a.1. 6 A(H1N1)pdm09 viruses were similar to the vaccine strain A/Victoria/4897/2022 and were classified as clade 6B.1A.5a.2a.1, one strain was related to the reference strain A/Sydney/5/2021 and assigned to clade 6B.1A.5a.2a.

ARVI detections. The overall proportion of respiratory samples tested positive for other ARVI (PIV, ADV, RSV, RhV, CoV, MPV, BoV) was estimated 11.8% of investigated samples by PCR.

Table 1. Results of influenza and other ARVI detection by RT-PCR in Russia, week 50 of 2025

COVID-19. According to the data obtained by NIC in Saint-Petersburg totally 14019 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 was detected in 530 (3.8%) cases.

Table 2. Results of influenza viruses isolation in Russia, week 50 of 2025

Sentinel influenza surveillance

Clinical samples from 31 SARI patients were investigated by rRT-PCR for influenza, among them 13 (41.9%) cases of influenza A(H3N2) were recognized. 3 (9.7%) of 31 SARI patients were positive for coronavirus SARS-CoV-2. Among 31 SARI samples 7 (22.6%) cases positive for ARVI were detected including: 1 case of PIV, 4 cases of CoV and 2 cases of BoV infection.

Clinical samples from 17 ILI/ARI patients were investigated for influenza, among them 4 (23.5%) cases of influenza A(H3N2) were recognized. Among 17 ILI/ARI samples 4 (23.5%) cases positive for ARVI were detected including: 1 case of PIV, 1 case of ADV, 1 case of RhV and 1 case of CoV infection. Among 17 ILI/ARI samples no positive cases of coronavirus SARS-CoV-2 were recognized.