NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION

week 20 of 2026 (11.05.26 - 17.05.26)

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 (39.2 per 10 000 of population) was lower than national baseline (82.9) by 52.7%.

Etiology of ILI & ARI. Among 5425 patients investigation 36 (0.7%) respiratory samples were positive for influenza, including 2 cases of unsubtyped influenza A in 2 cities, 8 cases of influenza A(H1N1)pdm09 in 3 cities, 2 cases of influenza A(H3N2) in 2 cities and 24 cases of influenza B in 5 cities. In Khabarovsk 2 cases of influenza C were confirmed by PCR during weeks 19 and 20 of 2026.

10 influenza viruses were isolated on MDCK cell culture, including: 9 influenza A(H1N1)pdm09 viruses in Moscow (3) and Saint-Petersburg (6) and 1 case of influenza B virus in Saint-Petersburg. Since the beginning of the season 1033 influenza viruses were isolated, including: 89 A(H1N1)pdm09 viruses, 934 A(H3N2) viruses and 10 influenza B viruses.

Antigenic characterization. Since the beginning of the season 2025-2026 627 influenza viruses have been antigenically characterized by the NICs in Saint-Petersburg and Moscow, including: 74 influenza A(H1N1)pdm09 viruses, 547 influenza A(H3N2) viruses and 6 influenza B viruses. 30 viruses A(H1N1)pdm09 were similar to the reference strains A/Victoria/4897/22 recommended in the vaccines for the Northern Hemisphere countries for the 2025-2026 season, 44 strains were a drift variant. 10 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, 525 A(H3N2) viruses were a drift variant, 11 viruses A(H3N2) were similar to the reference strain A/Thailand/8/2022, one strain was a drift variant of the reference strain A/Thailand/8/2022. 5 influenza B viruses were similar to the vaccine strain B/Austria/1359417/2021 and one strain was a drift variant of the reference strain B/Austria/1359417/2021.

Genetic characterization. Since the beginning of the season 2025-2026 sequenced 2081 influenza viruses in Saint-Petersburg. 1914 influenza A(H3N2) viruses were similar to the vaccine strain A/Croatia/10136RV/2023 and belonged to the 3C.2a1b.2a.2a.3a.1 clade, of which 1851 viruses belonged to subclade K, 31 as subclade J.2.x, 28 as subclade J.2.2 and 4 as subclade J.2.4. 157 A(H1N1)pdm09 viruses were similar to the vaccine strain A/Victoria/4897/2022 and were classified as clade 6B.1A.5a.2a.1, of which 21 viruses belonged to subclade D.3.1 and 136 viruses to subclade D.3.1.1. One strain was related to the reference strain A/Sydney/5/2021 and assigned to clade 6B.1A.5a.2a. 9 strain B viruses were similar to the vaccine strain B/Austria/1359417/2021 and were classified as clade V1A.3a.2.

Susceptibility to antivirals. Since the beginning of the season 2025-2026, the sensitivity of 437 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) were studied in NIC (Moscow, Saint-Petersburg), including: 25 influenza A(H1N1)pdm09 viruses, 411 influenza A(H3N2) viruses and 1 influenza B virus. 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 18.2% (PCR).

In sentinel surveillance system clinical samples from 9 SARI patients were investigated by rRT-PCR for influenza, among them no positive cases were recognized. Among 5 SARI samples no positive cases for coronavirus SARS-CoV-2 were recognized. Among 5 SARI samples 1 (20.0%) case positive for RSV infection.

Clinical samples from 5 ILI/ARI patient were investigated by rRT-PCR for influenza, among them no positive cases were recognized. Among 5 ILI/ARI samples 4 (80.0%) cases positive for ARVI were detected including: 1 case RhV and 3 cases of CoV infection. Among 5 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 7998 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 was detected in 75 (0.9%) cases.

Influenza and ARI morbidity data

Epidemiological data showed decrease of influenza and other ARI activity in Russia in comparison with previous week. The nationwide ILI and ARI morbidity level (39.2 per 10 000 of population) was lower than national baseline (82.9) by 52.7%.

Incidence rate of clinically diagnosed influenza decrease comparing to previous week and amounted to 0.075 per 10 000 of population, it was lower than pre-epidemic MEM baseline (0.45).

Hospitalization rate of clinically diagnosed influenza decreased comparing to previous week and amounted to 0.027 per 10 000 of population, it was lower 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 44 RBLs and two WHO NICs. According to these data as a result of 5425 patients investigation 36 (0.7%) respiratory samples were positive for influenza, including 2 cases of unsubtyped influenza A in 2 cities, 8 cases of influenza A(H1N1)pdm09 in 3 cities, 2 cases of influenza A(H3N2) in 2 cities and 24 cases of influenza B in 5 cities. In Khabarovsk 2 cases of influenza C were confirmed by PCR during weeks 19 and 20 of 2026.

10 influenza viruses were isolated on MDCK cell culture, including: 9 influenza A(H1N1)pdm09 viruses in Moscow (3) and Saint-Petersburg (6) and 1 case of influenza B virus in Saint-Petersburg. Since the beginning of the season 1033 influenza viruses were isolated, including: 89 A(H1N1)pdm09 viruses, 934 A(H3N2) viruses and 10 influenza B viruses.

Antigenic characterization. Since the beginning of the season 2025-2026 627 influenza viruses have been antigenically characterized by the NICs in Saint-Petersburg and Moscow, including: 74 influenza A(H1N1)pdm09 viruses, 547 influenza A(H3N2) viruses and 6 influenza B viruses. 30 viruses A(H1N1)pdm09 were similar to the reference strains A/Victoria/4897/22 recommended in the vaccines for the Northern Hemisphere countries for the 2025-2026 season, 44 strains were a drift variant. 10 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, 525 A(H3N2) viruses were a drift variant, 11 viruses A(H3N2) were similar to the reference strain A/Thailand/8/2022, one strain was a drift variant of the reference strain A/Thailand/8/2022. 5 influenza B viruses were similar to the vaccine strain B/Austria/1359417/2021 and one strain was a drift variant of the reference strain B/Austria/1359417/2021.

Genetic characterization. Since the beginning of the season 2025-2026 sequenced 2081 influenza viruses in Saint-Petersburg. 1914 influenza A(H3N2) viruses were similar to the vaccine strain A/Croatia/10136RV/2023 and belonged to the 3C.2a1b.2a.2a.3a.1 clade, of which 1851 viruses belonged to subclade K, 31 as subclade J.2.x, 28 as subclade J.2.2 and 4 as subclade J.2.4. 157 A(H1N1)pdm09 viruses were similar to the vaccine strain A/Victoria/4897/2022 and were classified as clade 6B.1A.5a.2a.1, of which 21 viruses belonged to subclade D.3.1 and 136 viruses to subclade D.3.1.1. One strain was related to the reference strain A/Sydney/5/2021 and assigned to clade 6B.1A.5a.2a. 9 strain B viruses were similar to the vaccine strain B/Austria/1359417/2021 and were classified as clade V1A.3a.2.

Susceptibility to antivirals. Since the beginning of the season 2025-2026, the sensitivity of 437 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) were studied in NIC (Moscow, Saint-Petersburg), including: 25 influenza A(H1N1)pdm09 viruses, 411 influenza A(H3N2) viruses and 1 influenza B virus. 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 18.2% of investigated samples by PCR.

Table 1. Results of influenza and other ARVI detection by RT-PCR in Russia, week 20 of 2026

COVID-19. According to the data obtained by NIC in Saint-Petersburg totally 7998 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 was detected in 75 (0.9%) cases.

Table 2. Results of influenza viruses isolation in Russia, week 20 of 2026

Sentinel influenza surveillance

Clinical samples from 9 SARI patients were investigated by rRT-PCR for influenza, among them no positive cases were recognized. Among 5 SARI samples no positive cases for coronavirus SARS-CoV-2 were recognized. Among 5 SARI samples 1 (20.0%) case positive for RSV infection.

Clinical samples from 5 ILI/ARI patient were investigated by rRT-PCR for influenza, among them no positive cases were recognized. Among 5 ILI/ARI samples 4 (80.0%) cases positive for ARVI were detected including: 1 case RhV and 3 cases of CoV infection. Among 5 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 20 of 2026, a decrease in incidence was observed. The situation is expected to improve in the coming weeks.