#17,187
The world is a big place, and as happens often, not everyone is seeing the same kind of flu season. Here in North America, and much of Europe, H3N2 is the dominant flu type this winter.
In fact, H3N2 has been the dominant flu strain here for the past two years, with the last major appearance of H1N1 just before the arrival of COVID in early 2020.
While 80% of the flu cases reported in the United States this winter have been H3N2, in Russia H1N1 reigns supreme (see map above). And as the following map from Flu News Europe reveals, they are seeing a very high incidence of flu.
This joint ECDC/WHO flu report states:
Weekly influenza overview
Week 49/2022 (05 December - 11 December 2022)
- The percentage of sentinel primary care specimens from patients presenting with ILI or ARI symptoms that tested positive for an influenza virus remained above the epidemic threshold (10%) and increased to 23% from 22% in the previous week.
- Influenza activity is increasing across the Region with 27 countries reporting widespread activity and/or medium to very-high intensity.
- Georgia, Germany, Italy, Kyrgyzstan, Lithuania, Portugal and Slovakia reported seasonal influenza activity above 40% positivity in sentinel primary care.
- Both influenza type A and type B viruses were detected with A(H3) viruses being dominant in sentinel surveillance systems but with A(H1)pdm09 viruses dominating in non-sentinel surveillance systems.
- Hospitalized patients with confirmed influenza virus infection were reported from ICU wards, other wards and SARI surveillance. Infections due to type A viruses dominated. Among 126 SARI cases, 17% were due to A(H3) and 57% due to A(H1)pdm09. The proportion of infections due to type A viruses continued to increase. This trend is driven largely by countries in the Eastern part of the region, in which the proportion of type B viruses is decreasing.
- When comparing the different influenza type distributions by system, it is important to consider that different sets of countries report to each system.
Qualitative indicators
For week 49/2022, of 38 countries and areas reporting on intensity of influenza activity, 8 reported baseline-intensity (across the Region), 10 reported low-intensity (across the Region), 14 reported medium-intensity (across the Region), 4 reported high-intensity (Kazakhstan, Lithuania, Malta and Slovakia) and 2 reported very high-intensity (Austria and Russian Federation).
Of 38 countries and areas reporting on geographic spread of influenza viruses, 2 reported no activity (Azerbaijan and Croatia), 7 reported sporadic spread (across the Region), 5 reported local spread (Lithuania, Malta, Serbia, Slovakia and United Kingdom (Northern Ireland)), 8 reported regional spread (across the Region) and 16 reported widespread activity (across the Region).
The following map from the weekly flu report from the Smorodintsev Research Institute of Influenza (WHO National Influenza Centre of Russia), illustrates that even within Russia, there is great deal of diversity in the type of flu viruses in circulation.
All of this matters because what happens in Russia, or Eastern Europe, doesn't necessarily stay there. Eventually, possibly this winter or perhaps next fall, H1N1 will return to Western Europe and North America.
And when it does, there is always the possibility that it will have picked up some significant antigenic changes while it was away.
Given the war in the Ukraine, and Russia's deteriorating diplomatic ties with the West, we may not get as much advance warning as we'd like. So it is worth paying attention to their winter epidemic as well as our own. This week's flu summary from Russia's RII follows.
NATIONAL WEEKLY INFLUENZA BULLETIN OF THE RUSSIAN FEDERATION
week 49 of 2022 (05.12.22 - 11.12.22)
Summary
Influenza and ARI incidence data. Influenza and other ARI activity increase of influenza and other ARI activity in Russia in comparison with previous week. The nationwide ILI and ARI morbidity level (143.6 per 10 000 of population) was higher than national baseline (70.0) by 105.1%.
Etiology of ILI & ARI. Among 7801 patients investigation 1549 (19.9%) respiratory samples were positive for influenza, including 1406 cases of influenza A(H1N1)pdm09 in 44 cities, 9 cases of influenza A(H3N2) in 3 cities, 49 cases of influenza A unsubtyped in 9 cities and 85 cases of influenza B in 20 cities.50 influenza viruses were isolated on MDCK cell culture, including: 44 influenza A(H1N1)pdm09 viruses in Astrakhan (7), Vladivostok (5), Voronezh (1), Moscow (11), Samara (1) and Saint-Petersburg (5), Chita (14) and 6 influenza B viruses in Samara (3), Chita (3). Since the beginning of the season, 151 viruses A(H1N1)pdm09 and 14 virus B have been isolated.
Antigenic characterization. Since the beginning of the season, 32 influenza A(H1N1)pdm09 have been antigenically characterized by the NICs, including: Moscow (21) and Saint-Petersburg (11) and 5 influenza B, including: Moscow (1) and Saint-Petersburg (4). All viruses A(H1N1)pdm09 were antigenically similar to reference strain A/Victoria/2570/2019 (H1N1)pdm09. 4 influenza B viruses were antigenically similar to reference strain В/Austria/1359417/2021 and 1 influenza B virus reacted with the reference virus antiserum to a 1:8 homologous titer.
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 18.6% (PCR).
In sentinel surveillance system clinical samples from 48 SARI patients were investigated by rRT-PCR for influenza, among them 9 (18.8%) cases of influenza A(H1N1)pdm09. 38 SARI patients were investigated for ARVI by rRT-PCR, among them 11 (28.9%) cases of ARVI recognized including 1 case of PIV, 5 cases of ADV, 1 case of RhV, 1 case of CoV, 2 cases of MPV and 1 case of BoV infection. Among 48 SARI patients no cases positive for coronavirus SARS-CoV-2 recognized.
Clinical samples from 67 ILI/ARI patients were investigated for influenza by rRT-PCR, among them 12 (17.9%) cases of influenza A(H1N1)pdm09. Among 58 ILI/ARI samples 6 (10.3%) cases positive for ARVI detected including 1 case of ADV, 2 cases of RhV, 1 case of CoV and 4 cases of BoV infection. 2 (3.0%) of 66 ILI/ARI patients were positive for coronavirus SARS-CoV-2.
COVID-19. Totally 21 692 870 cases and 392 832 deaths associated with COVID-19 were registered in Russia including 7 833 cases and 57 deaths in last 24 hours (on 12:00 of 15.12.2022). According to the data obtained by NIC in Saint-Petersburg totally 19 646 clinical samples were PCR investigated in last week. Among them coronavirus SARS-CoV-2 detected in 1076 (5.5%) cases.
