Epidemic Situation

NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION

week 20 of 2023 (15.05.23 - 21.05.23)

Summary

Influenza and ARI incidence data. Influenza and other ARI activity in Russia increase in comparison with previous week. The nationwide ILI and ARI morbidity level (43.6 per 10 000 of population) was lower than national baseline (70.0) by 37.7%.

Etiology of ILI & ARI. Among 4350 patients investigation 37 (0.9%) respiratory samples were positive for influenza, including 3 cases of influenza A unsubtyped in 3 cities, 1 case of influenza A(H1N1)pdm09 in 1 city, 3 cases of influenza A(H3N2) in 1 city and 30 cases of influenza B in 8 cities.

No influenza viruses were isolated on MDCK cell culture. Since the beginning of the season 1208 influenza viruses were isolated on MDCK cell culture, including: 777 viruses A(H1N1)pdm09, 30 viruses A(H3N2) and 401 viruses B.

Antigenic characterization. Since the beginning of the season, 657 influenza A(H1N1)pdm09 viruses have been antigenically characterized by the NICs, including: Moscow (105) and Saint-Petersburg (552), 29 influenza A(H3N2) viruses in Moscow (2) and Saint-Petersburg (27) and 211 influenza B, including: Moscow (15) and Saint-Petersburg (196). All viruses A(H1N1)pdm09 were antigenically similar to reference strain A/Victoria/2570/2019 (H1N1)pdm09. 27 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. 209 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 390 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in two NICs (Moscow, St. Petersburg), including 330 A(H1N1)pdm09 viruses and 10 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 14.9% (PCR).

In sentinel surveillance system clinical samples from 55 SARI patients were investigated by rRT-PCR for influenza, among them 1 (1.8%) influenza B case recognized. Among 53 SARI samples 6 (11.3%) cases positive for ARVI detected including 1 case of PIV, 2 cases of ADV, 2 cases of RhV and 1 case of BoV infection. 1 (1.8%) of 55 SARI patients were positive for coronavirus SARS-CoV-2.

Clinical samples from 22 ILI/ARI patients were investigated for influenza by rRT-PCR, among them no positive cases recognized. Among 22 ILI/ARI samples 3 (13.6%) cases positive for ARVI detected including 1 case of PIV, 1 case of RhV and 1 case of CoV infection. Among 20 ILI/ARI patients no positive cases of coronavirus SARS-CoV-2 recognized. 

COVID-19. Totally 22 917 873 cases and 398 919 deaths associated with COVID-19 were registered in Russia including 17 118 cases and 183 deaths in week 20. According to the data obtained by NIC in Saint-Petersburg totally 7040 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 383 (5.4%) 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 (43.6 per 10 000 of population) was lower than national baseline (70.0) by 37.7%.

Incidence rate of clinically diagnosed influenza decreased comparing to previous week and amounted to 0.053 per 10 000 of population, it was lower than pre-epidemic MEM baseline (0.060).

Hospitalization rate of clinically diagnosed influenza remained at the same level comparing to previous week and amounted to 0.017 per 10 000 of population, it was lower 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 46 RBLs and two WHO NICs. According to these data as a result of 4350 patients investigation 37 (0.9%) respiratory samples were positive for influenza, including 3 cases of influenza A unsubtyped in 3 cities, 1 case of influenza A(H1N1)pdm09 in 1 city, 3 cases of influenza A(H3N2) in 1 city and 30 cases of influenza B in 8 cities.

No influenza viruses were isolated on MDCK cell culture. Since the beginning of the season 1208 influenza viruses were isolated on MDCK cell culture, including: 777 viruses A(H1N1)pdm09, 30 viruses A(H3N2) and 401 viruses B.

Antigenic characterization. Since the beginning of the season, 657 influenza A(H1N1)pdm09 viruses have been antigenically characterized by the NICs, including: Moscow (105) and Saint-Petersburg (552), 29 influenza A(H3N2) viruses in Moscow (2) and Saint-Petersburg (27) and 211 influenza B, including: Moscow (15) and Saint-Petersburg (196). All viruses A(H1N1)pdm09 were antigenically similar to reference strain A/Victoria/2570/2019 (H1N1)pdm09. 27 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. 209 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 390 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in two NICs (Moscow, St. Petersburg), including 330 A(H1N1)pdm09 viruses and 10 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 14.9% of investigated samples by PCR.

Table 1. Results of influenza and other ARVI detection by RT-PCR in Russia, week 20 of 2023

COVID-19. Totally 22 917 873 cases and 398 919 deaths associated with COVID-19 were registered in Russia including 17 118 cases and 183 deaths in week 20. According to the data obtained by NIC in Saint-Petersburg totally 7040 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 383 (5.4%) cases.

Table 2. Results of influenza viruses isolation in Russia, week 20 of 2023

Sentinel influenza surveillance

Clinical samples from 55 SARI patients were investigated by rRT-PCR for influenza, among them 1 (1.8%) influenza B case recognized. Among 53 SARI samples 6 (11.3%) cases positive for ARVI detected including 1 case of PIV, 2 cases of ADV, 2 cases of RhV and 1 case of BoV infection. 1 (1.8%) of 55 SARI patients were positive for coronavirus SARS-CoV-2. 

Clinical samples from 22 ILI/ARI patients were investigated for influenza by rRT-PCR, among them no positive cases recognized. Among 22 ILI/ARI samples 3 (13.6%) cases positive for ARVI detected including 1 case of PIV, 1 case of RhV and 1 case of CoV infection. Among 20 ILI/ARI patients no positive cases of coronavirus SARS-CoV-2 recognized.