National Weekly Bulletin

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NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION

week 14 of 2024 (01.04.24 - 07.04.24)

Summary

Influenza and ARI incidence data. Influenza and other ARI activity in Russia decreased in comparison with previous week. The nationwide ILI and ARI morbidity level (53.1 per 10 000 of population) was lower than national baseline (70.0) by 24.1%.

Etiology of ILI & ARI. Among 8977 patients investigation 140 (1.6%) respiratory samples were positive for influenza, including no cases of influenza A(H1N1)pdm09, 26 cases of influenza A(H3N2) in 15 cities, 42 cases of unsubtyped influenza A in 6 ities and 72 cases of influenza B in 18 cities.

31 influenza viruses were isolated on MDCK cell culture, including: 1 case of influenza A(H1N1)pdm09 in Saint-Petersburg; 27 cases of influenza (H3N2) in Veliky Novgorod (4), Volgograd (1), Yekaterinburg (2), Moscow (3), Perm (2), Saint-Petersburg (15) and 3 cases of influenza B in Yekaterinburg (1), Moscow (1), Ulan-Ude (1). Since the beginning of the season 1082 influenza viruses were isolated on MDCK cell culture, including: 6 influenza viruses A(H1N1)pdm09, 1042 viruses A(H3N2) and 34 viruses B.

Antigenic characterization. Since the beginning of the season 679 influenza have been antigenically characterized by the NICs, including: 1 influenza A(H1N1)pdm09 virus, 660 influenza A(H3N2) viruses in Moscow (178) and Saint-Petersburg (482) and 18 influenza B viruses in Moscow (8) and Saint-Petersburg (10). Influenza A(H1N1)pdm09 virus was the drift-variant vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Victoria/4897/22 (H1N1)pdm09; 431 influenza (H3N2) viruses were antigenically similar to vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Darwin/09/2021 and 229 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). 11 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.2.3.1 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 457 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in two NICs (Moscow, Saint-Petersburg), including 456 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 20.0% (PCR).

In sentinel surveillance system clinical samples from 52 SARI patients were investigated by rRT-PCR for influenza, among them 3 (5.8%) cases of influenza A(H3N2) were detected. 4 (7.7%) of 52 SARI patients were positive for coronavirus SARS-CoV-2. Among 47 SARI samples 8 (17.0%) cases positive for ARVI were detected including: 1 case of PIV, 3 cases of RSV, 2 cases of RhV and 2 cases of MPV infection.

Clinical samples from 57 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 3 (5.3%) cases of influenza A(H3N2) were detected. Among 57 ILI/ARI samples 24 (42.1%) cases positive for ARVI were detected including: 4 cases of PIV, 3 cases of RSV, 10 cases of RhV, 4 cases of CoV and 3 cases of MPV infection. 6 (10.5%) of 57 ILI/ARI patients were positive for coronavirus SARS-CoV-2.

COVID-19. Totally 24 124 215 cases and 402 756 deaths associated with COVID-19 were registered in Russia including 19 954 cases and 69 deaths in week 14. According to the data obtained by NIC in Saint-Petersburg totally 10 803 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 627 (5.8%) 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 decreased of influenza and other ARI activity in Russia in comparison with previous week. The nationwide ILI and ARI morbidity level (53.1 per 10 000 of population) was lower than national baseline (70.0) by 24.1%.

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 decreased comparing to previous week and amounted to 0.12 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 decreased comparing to previous week and amounted to 0.028 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 8977 patients investigation 140 (1.6%) respiratory samples were positive for influenza, including no cases of influenza A(H1N1)pdm09, 26 cases of influenza A(H3N2) in 15 cities, 42 cases of unsubtyped influenza A in 6 ities and 72 cases of influenza B in 18 cities.

31 influenza viruses were isolated on MDCK cell culture, including: 1 case of influenza A(H1N1)pdm09 in Saint-Petersburg; 27 cases of influenza (H3N2) in Veliky Novgorod (4), Volgograd (1), Yekaterinburg (2), Moscow (3), Perm (2), Saint-Petersburg (15) and 3 cases of influenza B in Yekaterinburg (1), Moscow (1), Ulan-Ude (1). Since the beginning of the season 1082 influenza viruses were isolated on MDCK cell culture, including: 6 influenza viruses A(H1N1)pdm09, 1042 viruses A(H3N2) and 34 viruses B.

Antigenic characterization. Since the beginning of the season 679 influenza have been antigenically characterized by the NICs, including: 1 influenza A(H1N1)pdm09 virus, 660 influenza A(H3N2) viruses in Moscow (178) and Saint-Petersburg (482) and 18 influenza B viruses in Moscow (8) and Saint-Petersburg (10). Influenza A(H1N1)pdm09 virus was the drift-variant vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Victoria/4897/22 (H1N1)pdm09; 431 influenza (H3N2) viruses were antigenically similar to vaccine strain for the Northern Hemisphere countries for the 2023-2024 season A/Darwin/09/2021 and 229 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). 11 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.2.3.1 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 457 influenza viruses to neuraminidase inhibitors (oseltamivir, zanamivir) was studied in two NICs (Moscow, Saint-Petersburg), including 456 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.

Fig. 4. Geographic distribution of RT-PCR detected influenza viruses in cities under surveillance in Russia, week 14 of 2024
Fig. 4. Geographic distribution of RT-PCR detected influenza viruses in cities under surveillance in Russia, week 14 of 2024
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 20.0% 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 14 of 2024

  Number of  specimens / number of positive cases  % positive
Influenza
Number of specimens tested for influenza 8977 -
Influenza A (not subt.) 42 0,5%
Influenza A(H1)pdm09 0 0,0% 
Influenza A(H3) 26 0,3% 
Influenza B 72 0,8% 
All influenza 140 1,6%
Other ARVI
Number of specimens tested for ARVI 8851  -
PIV 195 2,2%
ADV 106 1,2%
RSV 338 3,8%
RhV 478 5,4%
CoV 347 3,9%
MPV 262 3,0%
BoV 41 0,5%
All ARVI 1767 20,0%
SARS-CoV-2 (COVID-19)
Number of specimens tested for SARS-CoV-2 10803 -
SARS-CoV-2 627 5,8%
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 24 124 215 cases and 402 756 deaths associated with COVID-19 were registered in Russia including 19 954 cases and 69 deaths in week 14. According to the data obtained by NIC in Saint-Petersburg totally 10 803 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 627 (5.8%) cases.

Table 2. Results of influenza viruses isolation in Russia, week 14 of 2024

  Number of specimens / number of viruses  % isolated viruses
Number of specimens 185 -
Influenza A(H1)pdm09 1 0,5% 
Influenza A(H3) 27 14,6% 
Influenza B 3 1,6% 
All influenza 31 16,8%

Sentinel influenza surveillance

Clinical samples from 52 SARI patients were investigated by rRT-PCR for influenza, among them 3 (5.8%) cases of influenza A(H3N2) were detected. 4 (7.7%) of 52 SARI patients were positive for coronavirus SARS-CoV-2. Among 47 SARI samples 8 (17.0%) cases positive for ARVI were detected including: 1 case of PIV, 3 cases of RSV, 2 cases of RhV and 2 cases of MPV infection.

Clinical samples from 57 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 3 (5.3%) cases of influenza B were detected. Among 57 ILI/ARI samples 24 (42.1%) cases positive for ARVI were detected including: 4 cases of PIV, 3 cases of RSV, 10 cases of RhV, 4 cases of CoV and 3 cases of MPV infection. 6 (10.5%) of 57 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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