ECDC: Influenza Virus Characterisation, November 2020

 

#15,614

It's no secret that since COVID-19 emerged - and people began wearing masks, ramped up their hand hygiene, and began practicing social distancing - influenza has practically dropped off the radar. We've seen similar drops in other infectious diseases, including Scarlet Fever in the UK, and AFM due to EV-D68 this fall in the United States. 

The latest global flu report from the WHO (Update 382) shows influenza in the Northern Hemisphere flatlined in March (see above graph), and remains barely detectable through November. 

While less flu is generally a generally good thing, particularly given the additional complications that can arise from a dual COVID-Influenza infection, it can have its downsides. 

• The lack of data (and virus isolates) means we have very little idea what evolutionary changes are occurring in flu strains circulating around the world. When seasonal flu returns - and there is no reason to believe it won't - we may find ourselves dealing with one or more antigenically drifted viruses.

• Another concern is, the longer we go without seeing seasonal influenza, the lower that community immunity is likely to drop.  Meaning that when influenza does return, our individual `shields' may be down or depressed, making us more susceptible to infection. 

• And while more theoretical, there is a line of thought that says that novel influenza pandemics are most likely to emerge during times of low community immunity (see PLoS Comp. Bio.: Spring & Early Summer Most Likely Time For A Pandemic).

Yesterday the ECDC published their 2nd monthly Influenza Characterization Report for the 2020-2021 flu season, and for the second month in a row they report:` . . . no shipments of influenza-positive specimens from European Union/European Economic Area (EU/EEA) countries have been received at the London WHO Collaborating Centre, the Francis Crick Worldwide Influenza Centre (WIC).'

Last month, the WHO urged member nations to continue their influenza surveillance programs and released a 48-page PDF file entitled:

Maintaining surveillance of influenza and monitoring SARS-CoV-2: adapting Global Influenza Surveillance and Response System (‎GISRS)‎ and sentinel systems during the COVID-19 pandemic: interim guidance, 8 November 2020

View/Open
WHO-2019-nCoV-Adapting_GISRS-2020.1-eng.pdf (‎1.916Mb)‎

Given the dearth of new information, I've only reproduced the ECDC's executive summary of their latest report.

Influenza virus characterisation - Summary Europe, November 2020

 

Surveillance report 8 Dec 2020

Publication series: Influenza Virus Characterisation 

ECDC’s influenza virus characterisation reports are published periodically and give an overview of circulating influenza viruses. They provide details on the current vaccine strains, summarise the development of the viruses since the last report, and closely follow the main developments for the ongoing influenza season. Virus characterisation reports are primarily intended for influenza virologists and epidemiologists.

Executive summary

This is the second report for the 2020–2021 influenza season. As of week 48/2020, only 288 influenza detections across the WHO European Region had been reported to TESSy; 52% type A viruses, with A(H3N2) prevailing over A(H1N1)pdm09, and 48% type B viruses with only two having been ascribed to a lineage, both being B/Victoria. This represents a 96% drop in detections compared to the same period in 2019, probably due to the COVID-19 pandemic and measures introduced to combat it.

Since the October 2020 characterisation report, no shipments of influenza-positive specimens from European Union/European Economic Area (EU/EEA) countries have been received at the London WHO Collaborating Centre, the Francis Crick Worldwide Influenza Centre (WIC). Therefore, this report focuses on genetic characterisation of influenza viruses with collection dates prior to the start, week 40, of weekly influenza surveillance reporting for the 2020-2021 influenza season.

The vast majority of A(H1N1)pdm09 viruses have continued to fall in genetic subclade 6B.1A5, mostly in the 6B.1A5A group with few in the 6B.1A5B group. 6B.1A5A viruses have continued to evolve and two subgroups have emerged designated 6B.1A5A+187V/A, representatives of which are recommended for use in the northern hemisphere 2020- 2021 season, and 6B.1A5A+156K, an antigenically distinct group representatives of which are recommended for use in the southern hemisphere 2021 season. Following a rise in the number of 6B.1A5A+156K viruses detected, the two subgroups appear to be circulating in approximately equal proportions currently, based on low numbers of viruses with collection dates after March 2020 having been detected and characterised genetically.

Recently circulating A(H3N2) viruses have continued to fall in clades 3C.2a and 3C.3a, with the vast majority of clade 3C.2a viruses being in the 3C.2a1b group which has now been divided into four subgroups designated 3C.2a1b+T131K-A, 3C.2a1b+T131K-B, 3C.2a1b+T135K-A and 3C.2a1b+T135K-B. Antisera raised in ferrets show high levels of clade/group specificity, although there is some subgroup cross-reactivity. Viruses representative of subgroup 3C.2a1b+T135K-B have been recommended for use in influenza vaccines for northern hemisphere 2020-2021 and southern hemisphere 2021 seasons. Of the low number of viruses with collection dates after March 2020 detected and characterised genetically, the majority have HA genes falling in subgroup 3C.2a1b+T131K-A.

 

Influenza virus characterisation, November 2020 - EN - [PDF-2.16 MB] 

Whether seasonal flu returns later this winter, next summer - or stays suppressed for a year or longer - we should be prepared for some surprises when it finally does return.