NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION

week 4 of 2026 (19.01.26 - 25.01.26)

Summary

Influenza and ARI incidence data. Influenza and other ARI activity in Russia decreased in comparison with previous week. The nationwide ILI and ARI morbidity level (53.0 per 10 000 of population) was lower than national baseline (82.9) by 36.1%.

Etiology of ILI & ARI. Among 8720 patients investigation 781 (9.0%) respiratory samples were positive for influenza, including 134 cases of unsubtyped influenza A in 6 cities, 9 cases of influenza A(H1N1)pdm09 in 5 cities, 632 cases of influenza A(H3N2) in 41 cities and 6 cases of influenza B in 4 cities.

51 influenza viruses A(H3N2) were isolated on MDCK cell culture in Astrakhan (3), Vologda (1), Yekaterinburg (3), Novosibirsk (5), Orenburg (1), Samara (8), Saint-Petersburg (21), Stavropol (8), Chita (1). Since the beginning of the season 549 influenza viruses, including: 4 A(H1N1)pdm09 viruses, 544 A(H3N2) viruses and 1 influenza B virus.

Antigenic characterization. Since the beginning of the season 2025-2026 241 influenza have been antigenically characterized by the NICs in Saint-Petersburg and Moscow, including: 2 influenza A(H1N1)pdm09 viruses and 239 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, second A(H1N1)pdm09 virus was a drift variant. 4 influenza A(H3N2) viruses were similar to the reference strain A/Croatia/10136RV/23, also recommended in vaccines for countries in the Northern Hemisphere for the 2025-2026 season, 223 A(H3N2) viruses were a 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 1359 influenza viruses in Saint-Petersburg. 1343 influenza A(H3N2) viruses were similar to the vaccine strain A/Croatia/10136RV/2023, of which 1293 viruses belong to clade 3C.2a1b.2a.2a.3a.1 subclade K, 50 viruses belong to clade 3C.2a1b.2a.2a.3a.1. 14 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. 1 strain B virus was similar to the vaccine strain B/Austria/1359417/2021 and was classified as clade V1A.3a.2.Susceptibility to antivirals. Since the beginning of the season 2025-2026, the sensitivity of 195 A(H3N2) influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) were studied in NIC (Saint-Petersburg). All studied viruses were sensitive to neuraminidase inhibitors.

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 11.2% (PCR).

In sentinel surveillance system clinical samples from 6 SARI patients were investigated by rRT-PCR for influenza, among them no positive cases were recognized. Among 6 SARI patient no positive cases of coronavirus SARS-CoV-2 were recognized. Among 6 ILI/ARI samples no positive cases for ARVI were recognized.

Clinical samples from 16 ILI/ARI patients were investigated by rRT-PCR for influenza, among them no positive cases were recognized. Among 16 ILI/ARI samples 2 (12.5%) cases positive for ARVI were detected including: 1 case of RhV, 1 case of CoV infection. Among 16 ILI/ARI samples no positive cases for coronavirus SARS-CoV-2 were recognized.

COVID-19. According to the data obtained by NIC in Saint-Petersburg totally 10326 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 was detected in 199 (1.9%) cases.

Influenza and ARI morbidity data

Epidemiological data showed decreased of influenza and other ARI activity in Russia in comparison with previous week. The nationwide ILI and ARI morbidity level (53.0 per 10 000 of population) was lower than national baseline (82.9) by 36.1%.

Incidence rate of clinically diagnosed influenza decreased comparing to previous week and amounted to 0.89 per 10 000 of population, it was higher than pre-epidemic MEM baseline (0.45).

Hospitalization rate of clinically diagnosed influenza decreased comparing to previous week and amounted to 0.21 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 46 RBLs and two WHO NICs. According to these data as a result of 8720 patients investigation 781 (9.0%) respiratory samples were positive for influenza, including 134 cases of unsubtyped influenza A in 6 cities, 9 cases of influenza A(H1N1)pdm09 in 5 cities, 632 cases of influenza A(H3N2) in 41 cities and 6 cases of influenza B in 4 cities.

51 influenza viruses A(H3N2) were isolated on MDCK cell culture in Astrakhan (3), Vologda (1), Yekaterinburg (3), Novosibirsk (5), Orenburg (1), Samara (8), Saint-Petersburg (21), Stavropol (8), Chita (1). Since the beginning of the season 549 influenza viruses, including: 4 A(H1N1)pdm09 viruses, 544 A(H3N2) viruses and 1 influenza B virus.Antigenic characterization. Since the beginning of the season 2025-2026 241 influenza have been antigenically characterized by the NICs in Saint-Petersburg and Moscow, including: 2 influenza A(H1N1)pdm09 viruses and 239 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, second A(H1N1)pdm09 virus was a drift variant. 4 influenza A(H3N2) viruses were similar to the reference strain A/Croatia/10136RV/23, also recommended in vaccines for countries in the Northern Hemisphere for the 2025-2026 season, 223 A(H3N2) viruses were a 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 1359 influenza viruses in Saint-Petersburg. 1343 influenza A(H3N2) viruses were similar to the vaccine strain A/Croatia/10136RV/2023, of which 1293 viruses belong to clade 3C.2a1b.2a.2a.3a.1 subclade K, 50 viruses belong to clade 3C.2a1b.2a.2a.3a.1. 14 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. 1 strain B virus was similar to the vaccine strain B/Austria/1359417/2021 and was classified as clade V1A.3a.2.Susceptibility to antivirals. Since the beginning of the season 2025-2026, the sensitivity of 195 A(H3N2) influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) were studied in NIC (Saint-Petersburg). All studied viruses were sensitive to neuraminidase inhibitors.

ARVI detections. The overall proportion of respiratory samples tested positive for other ARVI (PIV, ADV, RSV, RhV, CoV, MPV, BoV) was estimated 11.2% of investigated samples by PCR.

Table 1. Results of influenza and other ARVI detection by RT-PCR in Russia, week 4 of 2026

COVID-19. According to the data obtained by NIC in Saint-Petersburg totally 10326 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 was detected in 199 (1.9%) cases.

Table 2. Results of influenza viruses isolation in Russia, week 4 of 2026

Sentinel influenza surveillance

Clinical samples from 6 SARI patients were investigated by rRT-PCR for influenza, among them no positive cases were recognized. Among 6 SARI patient no positive cases of coronavirus SARS-CoV-2 were recognized. Among 6 ILI/ARI samples no positive cases for ARVI were recognized.

Clinical samples from 16 ILI/ARI patients were investigated by rRT-PCR for influenza, among them no positive cases were recognized. Among 16 ILI/ARI samples 2 (12.5%) cases positive for ARVI were detected including: 1 case of RhV, 1 case of CoV infection. Among 16 ILI/ARI samples no positive cases for coronavirus SARS-CoV-2 were recognized.

Influenza morbidity forecasting

An influenza incidence forecast was performed. The forecast is based on the Baroyan–Rvachev model. Model calibration was carried out using data on registered influenza and acute respiratory infection (ARI) cases, as well as laboratory influenza diagnostics (PCR), from the beginning of the epidemic season (week 40) up to the week preceding the publication of the forecast. The data are presented with a one-calendar-week time step. Optimal parameters were identified using calibration algorithms, resulting in the construction of a model curve. The estimated parameters allow the model curve to be extended and a forecast to be generated for the next four weeks from the observation date (the week for which the bulletin is published).

Fig. 13. Results of influenza incidence modeling, season 2025/26.

In week 04 of 2026, a decrease in incidence was observed. The situation is expected to improve in the coming weeks.