National Weekly Bulletin

NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION

week 48 of 2023 (27.11.23 - 03.12.23)

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 (98.1 per 10 000 of population) was higher than national baseline (70.0) by 40.1%.

Etiology of ILI & ARI. Among 12362 patients investigation 762 (6.2%) respiratory samples were positive for influenza, including 14 cases of influenza A(H1N1)pdm09 in 4 cities, 479 cases of influenza A(H3N2) in 24 cities, 262 cases of unsubtyped influenza A in 8 cities and 7 cases of influenza B in 6 cities.

22 influenza  viruses A(H3N2) were isolated on MDCK cell culture: in Moscow (NIC) (9), Samara (1), Saint- Petersburg (NIC) (9), Ulan-Ude (2), Khabarovsk (1). Since the beginning of the season 40 influenza viruses were isolated on MDCK cell culture, including 39 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 13.5% (PCR).

In sentinel surveillance system clinical samples from 48 SARI patients were investigated by rRT-PCR for influenza, among them no positive cases recognized. Among 43 SARI samples 2 (4.7%) cases of RhV infection. 1 (2.1%) of 48 SARI patients were positive for coronavirus SARS-CoV-2.

Clinical samples from 56 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 6 (10.7%) cases of influenza A(H3N2) were detected. Among 34 ILI/ARI samples 4 (11.8%) cases of RhV infection. 4 (7.3%) of 55 ILI/ARI patients were positive for coronavirus SARS-CoV-2.

COVID-19. Totally 23 430 629 cases and 400 716 deaths associated with COVID-19 were registered in Russia including 95 079 cases and 138 deaths in week 48. According to the data obtained by NIC in Saint-Petersburg totally 23 468 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 2135 (9.1%) 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 (98.1 per 10 000 of population) was higher than national baseline (70.0) by 40.1%.

Incidence rate of clinically diagnosed influenza increased comparing to previous week and amounted to 1.05 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 0.18 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 43 RBLs and two WHO NICs. According to these data as a result of 12362 patients investigation 762 (6.2%) respiratory samples were positive for influenza, including 14 cases of influenza A(H1N1)pdm09 in 4 cities, 479 cases of influenza A(H3N2) in 24 cities, 262 cases of unsubtyped influenza A in 8 cities and 7 cases of influenza B in 6 cities.

22 influenza viruses A(H3N2) were isolated on MDCK cell culture: in Moscow (NIC) (9), Samara (1), Saint- Petersburg (NIC) (9), Ulan-Ude (2), Khabarovsk (1). Since the beginning of the season 40 influenza viruses were isolated on MDCK cell culture, including 39 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 13.5% of investigated samples by PCR.

Table 1. Results of influenza and other ARVI detection by RT-PCR in Russia, week 48 of 2023

COVID-19. Totally 23 430 629 cases and 400 716 deaths associated with COVID-19 were registered in Russia including 95 079 cases and 138 deaths in week 48. According to the data obtained by NIC in Saint-Petersburg totally 23 468 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 2135 (9.1%) cases.

Table 2. Results of influenza viruses isolation in Russia, week 48 of 2023

Sentinel influenza surveillance

Clinical samples from 48 SARI patients were investigated by rRT-PCR for influenza, among them no positive cases recognized. Among 43 SARI samples 2 (4.7%) cases of RhV infection. 1 (2.1%) of 48 SARI patients were positive for coronavirus SARS-CoV-2. 

Clinical samples from 56 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 6 (10.7%) cases of influenza A(H3N2) were detected. Among 34 ILI/ARI samples 4 (11.8%) cases of RhV infection. 4 (7.3%) of 55 ILI/ARI patients were positive for coronavirus SARS-CoV-2.