NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION

week 13 of 2025 (24.03.25 - 30.03.25)

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 (78.4 per 10 000 of population) was lower than national baseline (89.9) by 12.8%.

Etiology of ILI & ARI. Among 13293 patients investigation 2242 (16.9%) respiratory samples were positive for influenza, including 416 cases of unsubtyped influenza A in 13 cities, 500 cases of influenza A(H1N1)pdm09 in 41 cities, 58 cases of influenza A(H3N2) in 14 cities and 1268 cases of influenza B in 44 cities.

44 influenza viruses were isolated on MDCK cell culture, including 17 cases of influenza A(H1N1)pdm09 in Astrakhan (1), Vladivostok (1), Yekaterinburg (6), Saint-Petersburg (1), Khabarovsk (7), Cheboksary (1), 2 cases of influenza A(H3N2) in Saint-Petersburg (1), Yekaterinburg (1) and 25 cases of influenza B in Astrakhan (2), Yekaterinburg (2), Novosibirsk (10), Orenburg (3), Saint-Petersburg (4), Khabarovsk (4). Since the beginning of the season 552 influenza viruses, including: 316 A(H1N1)pdm09 viruses, 15 - A(H3N2) and 221 influenza B viruses.

Antigenic characterization. Since the beginning of the season 275 influenza have been antigenically characterized by the NICs, including: 170 influenza A(H1N1)pdm09, 7 influenza A(H3N2) and 98 influenza B viruses. 168 A(H1N1)pdm09 viruses were similar to the reference strain A/Victoria/4897/22 recommended in the vaccines for the Northern Hemisphere countries for the 2024-2025 season, 2 A(H1N1)pdm09 strain reacted to a 1:8 homologous titer with serum to the vaccine strain. 6 A(H3N2) strain was similar to the vaccine strain A/Thailand/8/22, the other interacted to 1:8 homologous titer with serum to the A/Thailand/8/22 vaccine strain. 91 influenza B viruses were similar to the vaccine strain B/Austria/1359417/2021, 2 strains were drift variants and reacted to 1:8 homologous titer with serum to the vaccine strain.

Genetic analysis. Sequencing of 386 influenza A(H1N1)pdm09 viruses of the season 2024-2025 showed that all of them fell within clade 6B.1A.5a.2a, subclade C.1.9. 12 influenza A(H3N2) viruses belonged to clade 3c.2a1b.2a.2a.3a.1 (vaccine virus A/Thailand/8/2022-like), subclade J.2. 63 influenza B strains belonged to Victoria lineage, subclade V1A.3a.2 (B/Austria/1359417/2021-like). By genotypic testing all 461 influenza A and B viruses were susceptible to oseltamivir and zanamivir. 

Susceptibility to antivirals. Since the beginning of the season 2024-2025, the sensitivity of 198 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in NIC Saint-Petersburg, including: 130 A(H1N1)pdm09 influenza viruses, 3 A(H3N2) influenza viruses and 65 influenza B viruses. 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 12.1% (PCR).

In sentinel surveillance system clinical samples from 44 SARI patients were investigated by rRT-PCR for influenza, among them 7 (15.9%) cases of influenza were recognized, including: 4 cases of unsubtyped influenza A(H1N1)pdm09, 1 case of influenza A(H3N2) and 2 cases of influenza B B. 3 (6.8%) of 44 SARI patients were positive for coronavirus SARS-CoV-2. Among 44 SARI samples 5 (11.4%) cases positive for ARVI were detected, including: 3 cases of RSV and 2 cases of RhV infection.

Clinical samples from 24 ILI/ARI patients were investigated by rRT-PCR for influenza, among them 3 (12.5%) cases of influenza were recognized, including: 2 cases of influenza A(H1N1)pdm09 and 1 case of influenza B. Among 19 ILI/ARI samples 4 (21.1%) cases positive for ARVI were detected, including: 3 cases of PIV and 1 case of MPV infection. Among 24 ILI/ARI patients no positive cases of coronavirus SARS-CoV-2 recognized.

COVID-19. The Federal Operational Headquarters for Combating the Novel Coronavirus Infection has discontinued the publication of weekly COVID-19 morbidity reports starting from epidemiological week 12. This decision is due to the stabilization of the epidemiological situation regarding COVID-19 and the transition of the virus to the category of seasonal respiratory infections. According to the data obtained by NIC in Saint-Petersburg totally 14815 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 92 (0.6%) 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 (78.4 per 10 000 of population) was lower than national baseline (89.9) by 12.8%.

Incidence rate of clinically diagnosed influenza decreased comparing to previous week and amounted to 2.72 per 10 000 of population, it was higher than pre-epidemic MEM baseline (0.040).

Hospitalization rate of clinically diagnosed influenza decreased comparing to previous week and amounted to 0.51 per 10 000 of population, it was higher than pre-epidemic MEM baseline (0.010).

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 13293 patients investigation 2242 (16.9%) respiratory samples were positive for influenza, including 416 cases of unsubtyped influenza A in 13 cities, 500 cases of influenza A(H1N1)pdm09 in 41 cities, 58 cases of influenza A(H3N2) in 14 cities and 1268 cases of influenza B in 44 cities.

44 influenza viruses were isolated on MDCK cell culture, including 17 cases of influenza A(H1N1)pdm09 in Astrakhan (1), Vladivostok (1), Yekaterinburg (6), Saint-Petersburg (1), Khabarovsk (7), Cheboksary (1), 2 cases of influenza A(H3N2) in Saint-Petersburg (1), Yekaterinburg (1) and 25 cases of influenza B in Astrakhan (2), Yekaterinburg (2), Novosibirsk (10), Orenburg (3), Saint-Petersburg (4), Khabarovsk (4). Since the beginning of the season 552 influenza viruses, including: 316 A(H1N1)pdm09 viruses, 15 - A(H3N2) and 221 influenza B viruses.

Antigenic characterization. Since the beginning of the season 275 influenza have been antigenically characterized by the NICs, including: 170 influenza A(H1N1)pdm09, 7 influenza A(H3N2) and 98 influenza B viruses. 168 A(H1N1)pdm09 viruses were similar to the reference strain A/Victoria/4897/22 recommended in the vaccines for the Northern Hemisphere countries for the 2024-2025 season, 2 A(H1N1)pdm09 strain reacted to a 1:8 homologous titer with serum to the vaccine strain. 6 A(H3N2) strain was similar to the vaccine strain A/Thailand/8/22, the other interacted to 1:8 homologous titer with serum to the A/Thailand/8/22 vaccine strain. 91 influenza B viruses were similar to the vaccine strain B/Austria/1359417/2021, 2 strains were drift variants and reacted to 1:8 homologous titer with serum to the vaccine strain.

Genetic analysis. Sequencing of 386 influenza A(H1N1)pdm09 viruses of the season 2024-2025 showed that all of them fell within clade 6B.1A.5a.2a, subclade C.1.9. 12 influenza A(H3N2) viruses belonged to clade 3c.2a1b.2a.2a.3a.1 (vaccine virus A/Thailand/8/2022-like), subclade J.2. 63 influenza B strains belonged to Victoria lineage, subclade V1A.3a.2 (B/Austria/1359417/2021-like). By genotypic testing all 461 influenza A and B viruses were susceptible to oseltamivir and zanamivir. 

Susceptibility to antiviral. Since the beginning of the season 2024-2025, the sensitivity of 198 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in NIC Saint-Petersburg, including: 130 A(H1N1)pdm09 influenza viruses, 3 A(H3N2) influenza viruses and 65 influenza B viruses. 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) estimated as 12.1% of investigated samples by PCR.

Table 1. Results of influenza and other ARVI detection by RT-PCR in Russia, week 13 of 2025

COVID-19. The Federal Operational Headquarters for Combating the Novel Coronavirus Infection has discontinued the publication of weekly COVID-19 morbidity reports starting from epidemiological week 12. This decision is due to the stabilization of the epidemiological situation regarding COVID-19 and the transition of the virus to the category of seasonal respiratory infections. According to the data obtained by NIC in Saint-Petersburg totally 14815 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 92 (0.6%) cases.

Table 2. Results of influenza viruses isolation in Russia, week 13 of 2025

Sentinel influenza surveillance

Clinical samples from 44 SARI patients were investigated by rRT-PCR for influenza, among them 7 (15.9%) cases of influenza were recognized, including: 4 cases of unsubtyped influenza A(H1N1)pdm09, 1 case of influenza A(H3N2) and 2 cases of influenza B B. 3 (6.8%) of 44 SARI patients were positive for coronavirus SARS-CoV-2. Among 44 SARI samples 5 (11.4%) cases positive for ARVI were detected, including: 3 cases of RSV and 2 cases of RhV infection.

Clinical samples from 24 ILI/ARI patients were investigated by rRT-PCR for influenza, among them 3 (12.5%) cases of influenza were recognized, including: 2 cases of influenza A(H1N1)pdm09 and 1 case of influenza B. Among 19 ILI/ARI samples 4 (21.1%) cases positive for ARVI were detected, including: 3 cases of PIV and 1 case of MPV infection. Among 24 ILI/ARI patients no positive cases of coronavirus SARS-CoV-2 recognized.