National Weekly Bulletin

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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

Fig. 1. Influenza and ARVI morbidity in 61 cities under surveillance in Russia, seasons 2022/23 and 2023/24
Rates per 10 000 populationFig. 1. Influenza and ARVI morbidity in 61 cities under surveillance in Russia, seasons 2022/23 and 2023/24

Weeks

  • Morbidity 2023/24Morbidity 2023/24
  • Morbidity 2022/23Morbidity 2022/23
  • MEM baseline 2023/24MEM baseline 2023/24

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%.

Fig. 2. Comparative data on incidence rate of clinically diagnosed influenza, seasons 2022/23 and 2023/24
Rates per 10 000 populationFig. 2. Comparative data on incidence rate of clinically diagnosed influenza, seasons 2022/23 and 2023/24

Weeks

  • Season 2023/24Season 2023/24
  • Season 2022/23Season 2022/23
  • MEM baselineMEM baseline

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).

Fig. 3. Comparison of hospitalization rate with clinical diagnosis of influenza, seasons 2022/23 and 2023/24
Rates per 10 000 populationFig. 3. Comparison of hospitalization rate with clinical diagnosis of influenza, seasons 2022/23 and 2023/24

Weeks

  • Season 2023/24Season 2023/24
  • Season 2022/23Season 2022/23
  • MEM baselineMEM baseline

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.

Fig. 4. Geographic distribution of RT-PCR detected influenza viruses in cities under surveillance in Russia, week 48 of 2023
Fig. 4. Geographic distribution of RT-PCR detected influenza viruses in cities under surveillance in Russia, week 48 of 2023
PCR results
  • No dataNo data
  • No viruses detectedNo viruses detected
  • H1pdm09H1pdm09
  • H3H3
  • H3+H1pdm09H3+H1pdm09
  • BB
  • B+H1pdm09B+H1pdm09
  • B+H3B+H3
  • B+H3+H1pdm09B+H3+H1pdm09
  • A (not subt.)A (not subt.)
  • A (not subt.)+H1pdm09A (not subt.)+H1pdm09
  • A (not subt.)+H3A (not subt.)+H3
  • A (not subt.)+H3+H1pdm09A (not subt.)+H3+H1pdm09
  • A (not subt.)+BA (not subt.)+B
  • A (not subt.)+B+H1pdm09A (not subt.)+B+H1pdm09
  • A (not subt.)+B+H3A (not subt.)+B+H3
  • A (not subt.)+B+H3+H1pdm09A (not subt.)+B+H3+H1pdm09
Fig. 5. Monitoring of influenza viruses detection by RT-PCR in Russia, season 2023/24
Number of positive casesFig. 5. Monitoring of influenza viruses detection by RT-PCR in Russia, season 2023/24% positive

Weeks

  • H1pdm09H1pdm09
  • H3H3
  • BB
  • A (not subt.)A (not subt.)
  • % positive% positive
Fig. 6. Monitoring of ARVI detection by RT-PCR in Russia, season 2023/24
Number of positive casesFig. 6. Monitoring of ARVI detection by RT-PCR in Russia, season 2023/24

Weeks

  • PIVPIV
  • ADVADV
  • RSVRSV
  • RhVRhV
  • CoVCoV
  • MPVMPV
  • BoVBoV

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.

Fig. 7. Monitoring of influenza viruses isolation in Russia, season 2023/24
Number of positive casesFig. 7. Monitoring of influenza viruses isolation in Russia, season 2023/24% positive

Weeks

  • H1pdm09H1pdm09
  • H3H3
  • BB
  • % positive% positive

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

  Number of  specimens / number of positive cases  % positive
Influenza
Number of specimens tested for influenza 12362 -
Influenza A (not subt.) 262 2,1%
Influenza A(H1)pdm09 14 0,1% 
Influenza A(H3) 479 3,9% 
Influenza B 7 0,06% 
All influenza 762 6,2%
Other ARVI
Number of specimens tested for ARVI 12297  -
PIV 108 0,9%
ADV 206 1,7%
RSV 62 0,5%
RhV 617 5,0%
CoV 502 4,1%
MPV 63 0,5%
BoV 97 0,8%
All ARVI 1655 13,5%
SARS-CoV-2 (COVID-19)
Number of specimens tested for SARS-CoV-2 23468 -
SARS-CoV-2 2135 9,1%
Fig. 8. Results of PCR detections of SARS-CoV-2 in Russia
Fig. 8. Results of PCR detections of SARS-CoV-2 in Russia
% positive
  • No dataNo data
  • less then 10%less then 10%
  • 10-20%10-20%
  • 20-30%20-30%
  • 30-40%30-40%
  • 40-50%40-50%
  • 50% and more50% and more

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

  Number of specimens / number of viruses  % isolated viruses
Number of specimens 62 -
Influenza A(H1)pdm09 0 0,0% 
Influenza A(H3) 22 35,5% 
Influenza B 0 0,0% 
All influenza 22 35,5%

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.

Fig. 9. Monitoring of influenza viruses detection by RT-PCR among SARI patients in sentinel hospitals, season 2023/24
Number of positive casesFig. 9.  Monitoring of influenza viruses detection by RT-PCR among SARI patients in sentinel hospitals, season 2023/24% positive

Weeks

  • H1pdm09H1pdm09
  • H3H3
  • BB
  • A (not subt.)A (not subt.)
  • % positive% positive
Fig. 10. Monitoring of influenza viruses detection by RT-PCR among ILI/ARI patients in sentinel polyclinics, season 2023/24
Number of positive casesFig. 10.  Monitoring of influenza viruses detection by RT-PCR among ILI/ARI patients in sentinel polyclinics, season 2023/24% positive

Weeks

  • H1pdm09H1pdm09
  • H3H3
  • BB
  • A (not subt.)A (not subt.)
  • % positive% positive
Fig. 11. Monitoring of ARVI detection by RT-PCR among SARI patients in sentinel hospitals, season 2023/24
Number of positive casesFig. 11.  Monitoring of ARVI detection by RT-PCR among SARI patients in sentinel hospitals, season 2023/24

Weeks

  • PIVPIV
  • ADVADV
  • RSVRSV
  • RhVRhV
  • CoVCoV
  • MPVMPV
  • BoVBoV
Fig. 12. Monitoring of ARVI detection by RT-PCR among ILI/ARI patients in sentinel polyclinics, season 2023/24
Number of positive casesFig. 12.  Monitoring of ARVI detection by RT-PCR among ILI/ARI patients in sentinel polyclinics, season 2023/24

Weeks

  • PIVPIV
  • ADVADV
  • RSVRSV
  • RhVRhV
  • CoVCoV
  • MPVMPV
  • BoVBoV
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