National Weekly Bulletin

NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION

week 47 of 2023 (20.11.23 - 26.11.23)

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 (81.6 per 10 000 of population) was higher than national baseline (70.0) by 16.6%.

Etiology of ILI & ARI. Among 9715 patients investigation 317 (3.3%) respiratory samples were positive for influenza, including 7 cases of influenza A(H1N1)pdm09 in 4 cities, 244 cases of influenza A(H3N2) in 21 cities, 60 cases of unsubtyped influenza A in 5 cities and 6 cases of influenza B in 5 cities.

8 influenza  viruses were isolated on MDCK cell culture including 7 unfluenza AH3N2) viruses: in Moscow (NIC) (5), Ulan-Ude (2) and 1 influenza B virus in Khabarovsk. Since the beginning of the season 18 influenza viruses were isolated on MDCK cell culture, including 17 viruses A(H3N2) and 1 virus B.

Antigenic characterization. Since the beginning of the season 19 influenza A(H3N2) viruses has been antigenically characterized by the NICs, including: Moscow (2) and Saint-Petersburg (17). 16 influenza viruses were antigenically similar to vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Darwin/09/2021 and 3 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).

Genetic analysis. Since the beginning of the season 2022-2023, sequencing of 2237 influenza viruses and isolates from primary clinical materials from patients was performed by NIC (Saint-Petersburg). According to phylogenetic analysis, 1723 influenza A(H1N1)pdm09 viruses were assigned to genetic subgroup 6 B.1A.5a.2 and similar to reference virus A/Sydney/5/2021 (H1N1)pdm09; 64 A(H3N2) viruses was assigned to subgroup 3C.2a1b.2a.2, similar to reference virus Bangladesh/4005/2020 (H3N2); 13 was assigned to subgroup 3C.2a1b.2a.2а.1b and similar to reference virus A/Darwin/09/2021; 433 influenza type B viruses were assigned to genetic subgroup V1A.3a.2 reference virus B/Austria/1359417/2021.

Susceptibility to antivirals. Since the beginning of the season 2022-2023, the sensitivity of 708 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in two NICs (Moscow, St. Petersburg), including 533 A(H1N1)pdm09 viruses and 27 A(H3N2) viruses, 98 B viruses in NIC (Saint-Petersburg) and 45 A(H1N1)pdm09 viruses and 5 B viruses in NIC (Moscow). All viruses studied were sensitive to neuraminidase inhibitors, except for one A(H1N1)pdm09 strain and one influenza B virus that had reduced sensitivity to oseltamivir and 1 A(H1N1)pdm09 virus that showed resistance to oseltamivir and zanamivir.

According to genetic analysis conducted in St. Petersburg, 9 A(H1N1)pdm09 viruses had the H275Y substitution in neuraminidase responsible for resistance 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 13.4% (PCR).

In sentinel surveillance system clinical samples from 62 SARI patients were investigated by rRT-PCR for influenza, among them 4 (6.5%) cases of influenza A(H3N2) were detected. Among 57 SARI samples 7 (12.3%) cases positive for ARVI detected including 3 cases of PIV, 1 case of ADV and 3 cases of RhV infection. 5 (8.5%) of 59 SARI patients were positive for coronavirus SARS-CoV-2.

Clinical samples from 107 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 6 (5.6%) cases of influenza A(H3N2) were detected. Among 97 ILI/ARI samples 10 (10.3%) cases positive for ARVI detected including 3 cases of PIV, 2 cases of ADV and 5 cases of RhV infection. 10 (9.3%) of 107 ILI/ARI patients were positive for coronavirus SARS-CoV-2.

COVID-19. Totally 23 335 550 cases and 400 578 deaths associated with COVID-19 were registered in Russia including 77 106 cases and 90 deaths in week 47. According to the data obtained by NIC in Saint-Petersburg totally 15 872 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 1952 (12.3%) 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 (81.6 per 10 000 of population) was higher than national baseline (70.0) by 16.6%.

Incidence rate of clinically diagnosed influenza increased comparing to previous week and amounted to 0.35 per 10 000 of population, it was higher than pre-epidemic MEM baseline (0.060).

Hospitalization rate of clinically diagnosed influenza increased comparing to previous week and amounted to 0.068 per 10 000 of population, it was higher 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 44 RBLs and two WHO NICs. According to these data as a result of 9715 patients investigation 317 (3.3%) respiratory samples were positive for influenza, including 7 cases of influenza A(H1N1)pdm09 in 4 cities, 244 cases of influenza A(H3N2) in 21 cities, 60 cases of unsubtyped influenza A in 5 cities and 6 cases of influenza B in 5 cities.

8 influenza viruses were isolated on MDCK cell culture including 7 influenza A(H3N2) viruses: in Moscow (NIC) (5), Ulan-Ude (2) and 1 influenza B virus in Khabarovsk. Since the beginning of the season 18 influenza viruses were isolated on MDCK cell culture, including 17 viruses A(H3N2) and 1 virus B.

Antigenic characterization. Since the beginning of the season 19 influenza A(H3N2) viruses has been antigenically characterized by the NICs, including: Moscow (2) and Saint-Petersburg (17). 16 influenza viruses were antigenically similar to vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Darwin/09/2021 and 3 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).

Genetic analysis. Since the beginning of the season 2022-2023, sequencing of 2237 influenza viruses and isolates from primary clinical materials from patients was performed by NIC (Saint-Petersburg). According to phylogenetic analysis, 1723 influenza A(H1N1)pdm09 viruses were assigned to genetic subgroup 6 B.1A.5a.2 and similar to reference virus A/Sydney/5/2021 (H1N1)pdm09; 64 A(H3N2) viruses was assigned to subgroup 3C.2a1b.2a.2, similar to reference virus Bangladesh/4005/2020 (H3N2); 13 was assigned to subgroup 3C.2a1b.2a.2а.1b and similar to reference virus A/Darwin/09/2021; 433 influenza type B viruses were assigned to genetic subgroup V1A.3a.2 reference virus B/Austria/1359417/2021.

Susceptibility to antivirals. Since the beginning of the season 2022-2023, the sensitivity of 708 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in two NICs (Moscow, St. Petersburg), including 533 A(H1N1)pdm09 viruses and 27 A(H3N2) viruses, 98 B viruses in NIC (Saint-Petersburg) and 45 A(H1N1)pdm09 viruses and 5 B viruses in NIC (Moscow). All viruses studied were sensitive to neuraminidase inhibitors, except for one A(H1N1)pdm09 strain and one influenza B virus that had reduced sensitivity to oseltamivir and 1 A(H1N1)pdm09 virus that showed resistance to oseltamivir and zanamivir.

According to genetic analysis conducted in St. Petersburg, 9 A(H1N1)pdm09 viruses had the H275Y substitution in neuraminidase responsible for resistance to oseltamivir.

ARVI detections. The overall proportion of respiratory samples tested positive for other ARVI (PIV, ADV, RSV, RhV, CoV, MPV, BoV) estimated as 13.4% of investigated samples by PCR.

Table 1. Results of influenza and other ARVI detection by RT-PCR in Russia, week 47 of 2023

COVID-19. Totally 23 335 550 cases and 400 578 deaths associated with COVID-19 were registered in Russia including 77 106 cases and 90 deaths in week 47. According to the data obtained by NIC in Saint-Petersburg totally 15 872 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 1952 (12.3%) cases.

Table 2. Results of influenza viruses isolation in Russia, week 47 of 2023

Sentinel influenza surveillance

Clinical samples from 62 SARI patients were investigated by rRT-PCR for influenza, among them 4 (6.5%) cases of influenza A(H3N2) were detected. Among 57 SARI samples 7 (12.3%) cases positive for ARVI detected including 3 cases of PIV, 1 case of ADV and 3 cases of RhV infection. 5 (8.5%) of 59 SARI patients were positive for coronavirus SARS-CoV-2. 

Clinical samples from 107 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 6 (5.6%) cases of influenza A(H3N2) were detected. Among 97 ILI/ARI samples 10 (10.3%) cases positive for ARVI detected including 3 cases of PIV, 2 cases of ADV and 5 cases of RhV infection. 10 (9.3%) of 107 ILI/ARI patients were positive for coronavirus SARS-CoV-2.