National Weekly Bulletin

NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION

week 20 of 2024 (13.05.24 - 19.05.24)

Summary

Influenza and ARI incidence data. Influenza and other ARI activity in Russia increased in comparison with previous week. The nationwide ILI and ARI morbidity level (40.6 per 10 000 of population) was lower than national baseline (70.0) by 42.0%.

Etiology of ILI & ARI. Among 7101 patients investigation 70 (1.0%) respiratory samples were positive for influenza, including no cases of influenza A(H1N1)pdm09, no cases of influenza A(H3N2), 4 cases of unsubtyped influenza A in 3 Óities and 66 cases of influenza B in 17 cities.

No influenza viruses were isolated on MDCK cell culture. Since the beginning of the season 1150 influenza viruses were isolated on MDCK cell culture, including: 7 influenza viruses A(H1N1)pdm09, 1098 viruses A(H3N2) and 45 viruses B.

Antigenic characterization. Since the beginning of the season 751 influenza have been antigenically characterized by the NICs, including: 3 influenza A(H1N1)pdm09 viruses in Moscow (2) and Saint-Petersburg (1), 729 influenza A(H3N2) viruses in Moscow (186) and Saint-Petersburg (543) and 19 influenza B viruses in Moscow (8) and Saint-Petersburg (11). 2 influenza A(H1N1)pdm09 viruses were similar to the vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Victoria/4897/22 (H1N1)pdm09, 1 strain was its drift variant; 478 influenza á(H3N2) viruses were antigenically similar to vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Darwin/09/2021 and 251 viruses were a drift variant of the vaccine strain A/Darwin/09/2021 and reacted with antiserum to it in a reduced titer (1:8 and low). 12 influenza B viruses were antigenically similar to vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Austria/1359417/2021 and 7 were its drift variants.  

Genetic analysis. Since the beginning of the season 2023-2024, sequencing of 5 A(H1N1)pdm09 influenza isolates, 1364 influenza viruses and isolates from primary clinical materials from patients and 2 B influenza isolates were performed by NIC (Saint-Petersburg). According to phylogenetic analysis, 5 A(H1N1)pdm09 influenza isolates were assigned to genetic clade 6B.1A.5a.2a and similar to the vaccine strain A/Victoria/2570/2019, 1364 influenza A(H3N2) viruses were assigned to genetic clade 3C.2a1b.2a.2Á.3Á.1 and similar to the reference strain A/Thailand/08/2022, 1 virus was assigned to genetic clade 2a.3b and similar to the reference virus A/Sydney/732/2022, 2 B influenza isolates were assigned to genetic subclade 6B.1A.5a.2a and similar to the vaccine strain B/Austria/1359417/2021. All viruses were sensitive to neuraminidase inhibitors (oseltamivir, zanamivir).

Susceptibility to antivirals. Since the beginning of the season 2023-2024, the sensitivity of 509 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in two NICs (Moscow, Saint-Petersburg), including 508 A(H3N2) influenza viruses and 1 influenza B virus. All studied viruses were sensitive to neuraminidase inhibitors, except for one strain of A(H3N2) isolated in Moscow, which showed reduced sensitivity to oseltamivir.

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 17.0% (PCR).

In sentinel surveillance system clinical samples from 75 SARI patients were investigated by rRT-PCR for influenza, among them 3 (4.0%) cases of influenza B were detected. Among 75 SARI patients no positive cases for SARS-CoV-2 were detected. Among 71 SARI samples 5 (7.0%) cases positive for ARVI were detected including: 2 cases of RhV and 3 cases of MPV infection.

Clinical samples from 43 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 1 (2.3%) case of unsubtyped influenza A was detected. Among 34 ILI/ARI samples 7 (20.8%) cases positive for ARVI were detected including: 1 case of PIV, 5 cases of RhV and 1 case of MPV infection. 1 (2.3%) of 43 SARI patients was positive for coronavirus SARS-CoV-2.

COVID-19. Totally 24 206 892 cases and 403 045 deaths associated with COVID-19 were registered in Russia including 11 550 cases and 8 deaths in week 20. According to the data obtained by NIC in Saint-Petersburg totally 7941 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 335 (4.2%) cases.

Influenza and ARI morbidity data

Epidemiological data increased of influenza and other ARI activity in Russia in comparison with previous week. The nationwide ILI and ARI morbidity level (40.6 per 10 000 of population) was lower than national baseline (70.0) by 42.0%.

Incidence rate of clinically diagnosed influenza increased comparing to previous week and amounted to 0.069 per 10 000 of population, it was higher 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 0.014 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 45 RBLs and two WHO NICs. According to these data as a result of 7101 patients investigation 70 (1.0%) respiratory samples were positive for influenza, including no cases of influenza A(H1N1)pdm09, no cases of influenza A(H3N2), 4 cases of unsubtyped influenza A in 3 Óities and 66 cases of influenza B in 17 cities.

No influenza viruses were isolated on MDCK cell culture. Since the beginning of the season 1150 influenza viruses were isolated on MDCK cell culture, including: 7 influenza viruses A(H1N1)pdm09, 1098 viruses A(H3N2) and 45 viruses B.

Antigenic characterization. Since the beginning of the season 751 influenza have been antigenically characterized by the NICs, including: 3 influenza A(H1N1)pdm09 viruses in Moscow (2) and Saint-Petersburg (1), 729 influenza A(H3N2) viruses in Moscow (186) and Saint-Petersburg (543) and 19 influenza B viruses in Moscow (8) and Saint-Petersburg (11). 2 influenza A(H1N1)pdm09 viruses were similar to the vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Victoria/4897/22 (H1N1)pdm09, 1 strain was its drift variant; 478 influenza á(H3N2) viruses were antigenically similar to vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Darwin/09/2021 and 251 viruses were a drift variant of the vaccine strain A/Darwin/09/2021 and reacted with antiserum to it in a reduced titer (1:8 and low). 12 influenza B viruses were antigenically similar to vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Austria/1359417/2021 and 7 were its drift variants. 

Genetic analysis. Since the beginning of the season 2023-2024, sequencing of 5 A(H1N1)pdm09 influenza isolates, 1364 influenza viruses and isolates from primary clinical materials from patients and 2 B influenza isolates were performed by NIC (Saint-Petersburg). According to phylogenetic analysis, 5 A(H1N1)pdm09 influenza isolates were assigned to genetic clade 6B.1A.5a.2a and similar to the vaccine strain A/Victoria/2570/2019, 1364 influenza A(H3N2) viruses were assigned to genetic clade 3C.2a1b.2a.2Á.3Á.1 and similar to the reference strain A/Thailand/08/2022, 1 virus was assigned to genetic clade 2a.3b and similar to the reference virus A/Sydney/732/2022, 2 B influenza isolates were assigned to genetic subclade 6B.1A.5a.2a and similar to the vaccine strain B/Austria/1359417/2021. All viruses were sensitive to neuraminidase inhibitors (oseltamivir, zanamivir).

Susceptibility to antivirals. Since the beginning of the season 2023-2024, the sensitivity of 509 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in two NICs (Moscow, Saint-Petersburg), including 508 A(H3N2) influenza viruses and 1 influenza B virus. All studied viruses were sensitive to neuraminidase inhibitors, except for one strain of A(H3N2) isolated in Moscow, which showed reduced sensitivity to oseltamivir.

ARVI detections. The overall proportion of respiratory samples tested positive for other ARVI (PIV, ADV, RSV, RhV, CoV, MPV, BoV) estimated as 17.0% of investigated samples by PCR.

Table 1. Results of influenza and other ARVI detection by RT-PCR in Russia, week 20 of 2024

COVID-19. Totally 24 206 892 cases and 403 045 deaths associated with COVID-19 were registered in Russia including 11 550 cases and 8 deaths in week 20. According to the data obtained by NIC in Saint-Petersburg totally 7941 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 335 (4.2%) cases.

Table 2. Results of influenza viruses isolation in Russia, week 20 of 2024

Sentinel influenza surveillance

Clinical samples from 75 SARI patients were investigated by rRT-PCR for influenza, among them 3 (4.0%) cases of influenza B were detected. Among 75 SARI patients no positive cases for SARS-CoV-2 were detected. Among 71 SARI samples 5 (7.0%) cases positive for ARVI were detected including: 2 cases of RhV and 3 cases of MPV infection.

Clinical samples from 43 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 1 (2.3%) case of unsubtyped influenza A was detected. Among 34 ILI/ARI samples 7 (20.8%) cases positive for ARVI were detected including: 1 case of PIV, 5 cases of RhV and 1 case of MPV infection. 1 (2.3%) of 43 SARI patients was positive for coronavirus SARS-CoV-2.