Epidemic Situation

NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION

week 11 of 2023 (13.03.23 - 19.03.23)

Summary

Influenza and ARI incidence data. Influenza and other ARI activity increase of influenza and other ARI activity in Russia in comparison with previous week. The nationwide ILI and ARI morbidity level (72.3 per 10 000 of population) was higher than national baseline (70.0) by 3.3%.

Etiology of ILI & ARI. Among 8023 patients investigation 444 (5.5%) respiratory samples were positive for influenza, including 9 cases of influenza A(H1N1)pdm09 in 5 cities, 2 cases of influenza A(H3N2) in 2 cities, 8 cases of influenza A unsubtyped in 4 cities and 425 cases of influenza B in 41 cities.

52 influenza viruses were isolated on MDCK cell culture, including: 4 influenza A(H1N1)pdm09 viruses in Birobidzhan (2), Yekaterinburg (1), Tomsk (1); 1 influenza A(H3N2) virus in Birobidzhan; 47 influenza B viruses in Astrakhan (3), Birobidzhan (2), Yekaterinburg (2), Novosibirsk (1), Saint-Petersburg (19), Khabarovsk (20). Since the beginning of the season 1088 influenza viruses were isolated on MDCK cell culture, including: 701 viruses A(H1N1)pdm09, 28 viruses A(H3N2) and 359 viruses B.

Antigenic characterization. Since the beginning of the season, 559 influenza A(H1N1)pdm09 viruses have been antigenically characterized by the NICs, including: Moscow (98) and Saint-Petersburg (461), 28 influenza A(H3N2) viruses in Moscow (1) and Saint-Petersburg (27) and 113 influenza B, including: Moscow (10) and Saint-Petersburg (103). All viruses A(H1N1)pdm09 were antigenically similar to reference strain A/Victoria/2570/2019 (H1N1)pdm09. 26 influenza A(H3N2) strains were similar to the reference virus A/Darwin/9/2021 and 2 influenza A(H3N2) viruses reacted with the reference virus antiserum to a 1:8 homologous titer. 111 influenza B viruses were antigenically similar to reference strain В/Austria/1359417/2021 and 2 influenza B viruses reacted with the reference virus antiserum to a 1:8 homologous titer.

Genetic analysis. Sequencing of 993 influenza viruses and isolates from primary clinical materials from patients was performed by NIC (Saint-Petersburg). According to phylogenetic analysis, 904 influenza A(H1N1)pdm09 viruses were assigned to genetic subgroup 6 B.1A.5a.2 and similar to reference virus A/Victoria/2570/2019 (H1N1)pdm09; 27 A(H3N2) viruses was assigned to subgroup 3C.2 a1b.2a.2 and similar to reference virus Bangladesh/4005/2020 (H3N2); 62 influenza type B viruses were assigned to genetic subgroup V1A.3a.2 reference virus B/Austria/1359417/2021.Susceptibility to antivirals. The sensitivity of 280 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in two NICs (Moscow, St. Petersburg), including 224 A(H1N1)pdm09 viruses and 6 A(H3N2) viruses in NIC (Saint-Petersburg) and 45 A(H1N1)pdm09 viruses and 5 B viruses in NIC (Moscow). All the viruses studied were sensitive to oseltamivir and zanamivir.

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 10.0% (PCR).

In sentinel surveillance system clinical samples from 99 SARI patients were investigated by rRT-PCR for influenza, among them 2 (2.0%) cases of influenza, including 1 case of influenza A(H1N1)pdm09 and 1 case of influenza A(H3N2). Among 89 SARI samples 14 (15.7%) cases positive for ARVI detected including 1 case of ADV, 4 cases of RSV, 1 case of RhV, 1 case of CoV, 6 cases of MPV and 1 case of BoV infection. 2 (2.0%) of 99 SARI patients were positive for coronavirus SARS-CoV-2. 

Clinical samples from 58 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 2 (3.4%) cases of influenza, including 1 case of influenza A unsubtyped and 1 case of influenza B. Among 47 ILI/ARI samples 10 (21.3%) cases positive for ARVI detected including 2 cases of ADV, 5 cases of CoV and 3 cases of MPV infection. 7 (13.2%) of 53 ILI/ARI patients were positive for coronavirus SARS-CoV-2.  

COVID-19. Totally 22 550 395 cases and 396 974 deaths associated with COVID-19 were registered in Russia including 12 512 cases and 36 deaths in last 24 hours (on 12:00 of 23.03.2023). According to the data obtained by NIC in Saint-Petersburg totally 12 728 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 1873 (14.7%) cases.

Influenza and ARI morbidity data

Epidemiological data showed increase of influenza and other ARI activity in Russia in comparison with previous week. The nationwide ILI and ARI morbidity level (72.3 per 10 000 of population) was higher than national baseline (70.0) by 3.3%.

Incidence rate of clinically diagnosed influenza increased comparing to previous week and amounted to 0.56 per 10 000 of population, it was higer than pre-epidemic MEM baseline (0.060).

Hospitalization rate of clinically diagnosed influenza decreased comparing to previous week and amounted to 0.11 per 10 000 of population, it was higer than pre-epidemic MEM baseline (0.040).

Influenza and ARVI laboratory testing results

Cumulative results of influenza laboratory diagnosis by rRT-PCR were submitted by 49 RBLs and two WHO NICs. According to these data as a result of 8023 patients investigation 444 (5.5%) respiratory samples were positive for influenza, including 9 cases of influenza A(H1N1)pdm09 in 5 cities, 2 cases of influenza A(H3N2) in 2 cities, 8 cases of influenza A unsubtyped in 4 cities and 425 cases of influenza B in 41 cities.

52 influenza viruses were isolated on MDCK cell culture, including: 4 influenza A(H1N1)pdm09 viruses in Birobidzhan (2), Yekaterinburg (1), Tomsk (1); 1 influenza A(H3N2) virus in Birobidzhan; 47 influenza B viruses in Astrakhan (3), Birobidzhan (2), Yekaterinburg (2), Novosibirsk (1), Saint-Petersburg (19), Khabarovsk (20). Since the beginning of the season 1088 influenza viruses were isolated on MDCK cell culture, including: 701 viruses A(H1N1)pdm09, 28 viruses A(H3N2) and 359 viruses B.

Antigenic characterization. Since the beginning of the season, 559 influenza A(H1N1)pdm09 viruses have been antigenically characterized by the NICs, including: Moscow (98) and Saint-Petersburg (461), 28 influenza A(H3N2) viruses in Moscow (1) and Saint-Petersburg (27) and 113 influenza B, including: Moscow (10) and Saint-Petersburg (103). All viruses A(H1N1)pdm09 were antigenically similar to reference strain A/Victoria/2570/2019 (H1N1)pdm09. 26 influenza A(H3N2) strains were similar to the reference virus A/Darwin/9/2021 and 2 influenza A(H3N2) viruses reacted with the reference virus antiserum to a 1:8 homologous titer. 111 influenza B viruses were antigenically similar to reference strain В/Austria/1359417/2021 and 2 influenza B viruses reacted with the reference virus antiserum to a 1:8 homologous titer.Genetic analysis. Sequencing of 993 influenza viruses and isolates from primary clinical materials from patients was performed by NIC (Saint-Petersburg). According to phylogenetic analysis, 904 influenza A(H1N1)pdm09 viruses were assigned to genetic subgroup 6 B.1A.5a.2 and similar to reference virus A/Victoria/2570/2019 (H1N1)pdm09; 27 A(H3N2) viruses was assigned to subgroup 3C.2 a1b.2a.2 and similar to reference virus Bangladesh/4005/2020 (H3N2); 62 influenza type B viruses were assigned to genetic subgroup V1A.3a.2 reference virus B/Austria/1359417/2021.Susceptibility to antivirals. The sensitivity of 280 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in two NICs (Moscow, St. Petersburg), including 224 A(H1N1)pdm09 viruses and 6 A(H3N2) viruses in NIC (Saint-Petersburg) and 45 A(H1N1)pdm09 viruses and 5 B viruses in NIC (Moscow). All the viruses studied were sensitive to oseltamivir and zanamivir.

ARVI detections. The overall proportion of respiratory samples tested positive for other ARVI (PIV, ADV, RSV, RhV, CoV, MPV, BoV) estimated as 10.0% of investigated samples by PCR.

Table 1. Results of influenza and other ARVI detection by RT-PCR in Russia, week 11 of 2023

COVID-19. Totally 22 550 395 cases and 396 974 deaths associated with COVID-19 were registered in Russia including 12 512 cases and 36 deaths in last 24 hours (on 12:00 of 23.03.2023). According to the data obtained by NIC in Saint-Petersburg totally 12 728 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 1873 (14.7%) cases.

Table 2. Results of influenza viruses isolation in Russia, week 11 of 2023

Sentinel influenza surveillance

Clinical samples from 99 SARI patients were investigated by rRT-PCR for influenza, among them 2 (2.0%) cases of influenza, including 1 case of influenza A(H1N1)pdm09 and 1 case of influenza A(H3N2). Among 89 SARI samples 14 (15.7%) cases positive for ARVI detected including 1 case of ADV, 4 cases of RSV, 1 case of RhV, 1 case of CoV, 6 cases of MPV and 1 case of BoV infection. 2 (2.0%) of 99 SARI patients were positive for coronavirus SARS-CoV-2. 

Clinical samples from 58 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 2 (3.4%) cases of influenza, including 1 case of influenza A unsubtyped and 1 case of influenza B. Among 47 ILI/ARI samples 10 (21.3%) cases positive for ARVI detected including 2 cases of ADV, 5 cases of CoV and 3 cases of MPV infection. 7 (13.2%) of 53 ILI/ARI patients were positive for coronavirus SARS-CoV-2.