Russia Reporting A Late Season Surge In H1N1

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Two months ago, in Russia As An Outlier in This Year's Flu Epidemic, we looked at what had been (up to epi week 2) a lackluster flu season in Russia. In late January the rate of ILI & ARI morbidity was nearly 30% below the baseline for that time of year.

By mid-February (epi week 6_, in Russia : A Late Season Flu Surge & 3 NAI Resistant H1N1 Viruses, we saw the ILI & ARI rate finally exceed the baseline (by 6.6%) for the first time this winter. 

By last week (week 10) - after appearing to peak the previous week - the rate fell below the baseline once again.  Now last week's report appears to have been in error or complete, as week 11 has once again jumped to the highest level of activity (94.6 per 10 000 of population) for the season (30.3% over baseline). 

While a far cry from the severe season of 2016, this is the highest level of flu activity to be reported this late in March by the Russian Institute of Influenza in the past 7 years. 

Two months ago, the dominant strain in Russia was A(H3N2), while today H1N1 has now pulled into the lead. 

Given the atypical flu seasons we've been seeing the past 12 months around the globe (summer H3N2 outbreaks in Hong Kong & China, followed by Influenza B this winter, and back-to-back H3N2 seasons in the Northern Hemisphere), the unusually mild, and late arriving flu season in Russia this winter is worth noting. 

Some excerpts from this week's Russian Influenza Epidemiological Report (Week 11) follow:

Conclusion

Influenza and ARI morbidity data. Increase of influenza and other ARI activity was registered during week 11.2018 in Russia. The ILI & ARI incidence rate (94.6 per 10 000 of population) was above by 30.3% the nationalwide baseline.

Etiology of ILI & ARI morbidity. The overall percent of respiratory samples positive for influenza was estimated as 26.5%. Proportion of influenza A(H1N1)pdm09, A(H3N2), type A and type B viruses was estimated as 38.4%, 24.8%, 2.6% and 34.1%, respectively.

Antigenic characterization. 222 influenza viruses were characterized antigenically in Moscow and Saint-Petersburg NICs, including 65 influenza A(H1N1)pdm09 viruses, 44 influenza A(H3N2) strains and 113 influenza type B strains.

All influenza A(H1N1)pdm09 strains were related to influenza A/Michigan/45/2015, influenza A(H3N2) strains to A/Hong Kong/4801/2014 viruses. 97 influenza type B strains belonged to Yamagata lineage and were like B/Phuket/3073/2013 reference virus, 6 influenza type B strains belonged to Victoria lineage and were antigenically related to B/Brisbain/60/2008 strain.

Genetic characterization. Full-genome NGS of 58 influenza positive samples and viruses from 6 cities was conducted. 16 influenza A(H1N1)pdm09 viruses belonged to phylogenetic group 6B.1 with amino acid substitutions in HA S84N, S162N and I216T.

According to phylogenetic analisis of HA 18 of 22 tested influenza A(H3N2) viruses belonged to clade 3C.2a carring aa substitutions L3I, N144S, F159Y, K160T, N225D and Q311H in HA1. Four influenza A(H3N2) viruses belonged to genetic subgroup 3C.2a1 and carried aa substitutions K92R, N121K, T135K and H311Q.

2 influenza B viruses of Victoria-lineage belonged to genetic subgroup 1A (B/Brisbane/60/2008-like). All 18 influenza B viruses of Yamagata-lineage belonged to clade 3 (B/Phuket/3073/2013-like) and had substitution L172Q and M251V in HA1.

Susceptibility to antivirals.Most viruses were susceptible to NA inhibitors excluding three influenza A(H1N1)pdm09 strains isolated in Moscow which had H275Y amino acid substitution in NA responsible for highly reduced susceptibility to oseltamivir and zanamivir.

14 influenza strains tested in MUNANA-assay for antiviral resistance to NA inhibitors in RII NIC, including 3 A(H1N1)pdm09 strains isolated in St.Petersburg, 4 A(H3N2), two B Victoria strains and 5 B Yamagata viruses were susceptible to oseltamivir and zanamivir. All influenza A strains tested were resistant to rimantadine.

Percent of positive ARI cases of non-influenza etiology (PIV, adeno- and RSV) was estimated as 18.3% of investigated patients by IFA and 8.3% by PCR. Last weeks RSV dominated among ARI agents.

In sentinel surveillance system clinical samples from 144 SARI and ILI/ARI patients were investigated by rRT-PCR. 35 (44.3%) influenza cases were detected among SARI patients, including 8 influenza A(H1N1)pdm09 cases, 16 influenza A(H3N2) cases and 11 influenza B cases. Among ILI/ARI patients 20 (30.8%) influenza cases were detected, including 4 influenza A(H1N1)pdm09, 8 influenza A(H3N2) and 8 influenza B cases.

This late season surge in influenza activity - particularly in countries bordering Russia - has also been noted in the latest Joint ECDC - WHO/Europe weekly influenza Update.

Week 10/2018 (5-11 March 2018)

• Influenza viruses continue to circulate widely in the Region, apart from some eastern European countries that have only recently reported increased activity.
  
• Similar to the previous week, 50% of the individuals sampled from primary healthcare settings tested positive for influenza virus, despite the peak rate for the Region occurring in week 05/2018.
  
• Both influenza virus types A and B were co-circulating with a higher proportion of type B viruses and with B/Yamagata continuing to be the dominant lineage.
  
• Similar proportions of influenza type A and B viruses were reported in patients admitted to ICU, while the majority of severe cases reported this season have been due to influenza type B and occur in persons above the age of 15 years.
  

Although the Northern Hemisphere's flu season is clearly winding down, what happens over the next few weeks could still have some influence over what happens in the upcoming Southern Hemisphere flu season.