#16,505
Due to the COVID pandemic - and the strict social distancing measures taken globally to contain it - reports of seasonal influenza nearly disappeared in March of 2020, and only began to reemerge last November (see CDC HAN # 00458 : Increasing Seasonal Influenza A (H3N2) Activity).
During this lull, reference laboratories reported a 99% drop in influenza samples submitted for sequencing (see ECDC: Influenza Virus Characterisation - July 2021), raising concerns over our ability to detect changes in the virus which might affect this year's vaccine effectiveness.
In recent weeks we've seen reports suggesting this year's A/H3N2 virus - which appears to be dominant globally - may have drifted antigenically enough to impact vaccine effectiveness (see Preprint: Antigenic & Virological properties of an H3N2 Variant That Will Likely Dominate the 2021-2022 Influenza season).
The return of seasonal influenza - alongside COVID - also raises concerns over coinfections with the pandemic coronavirus and flu, although studies on its impact are limited (see Clinical and virological impact of single and dual infections with influenza A (H1N1) and SARS-CoV-2 in adult inpatients).
Three weeks ago, in WHO Europe: Influenza Season Has Begun, we saw the first confirmation of influenza's return to Europe, and today we have the latest WHO Global Influenza Update (#410), current through December 26th.
Influenza Update N° 410
10 January 2022, based on data up to 26 December 2021
Information in this report is categorized by influenza transmission zones, which are geographical groups of countries, areas or territories with similar influenza transmission patterns. For more information on influenza transmission zones, see the link below:
Influenza Transmission Zones (pdf, 659kb)
- The current influenza surveillance data should be interpreted with caution as the ongoing COVID-19 pandemic has influenced to varying extents health seeking behaviours, staffing/routines in sentinel sites, as well as testing priorities and capacities in Member States. Various hygiene and physical distancing measures implemented by Member States to reduce SARS-CoV-2 virus transmission have likely played a role in reducing influenza virus transmission.
- Globally, influenza activity remains low but continued to increase especially in the temperate zones of the northern hemisphere. In several countries influenza activity reached the levels seen this time of year in pre-COVID-19 period.
- With the increasing detections of influenza during COVID-19 pandemic, countries are recommended to prepare for co-circulation of influenza and SARS-CoV-2. They are encouraged to enhance integrated surveillance to monitor influenza and SARS-CoV-2 at the same time, and step-up their influenza vaccination campaign to prevent severe disease and hospitalizations. Clinicians should consider influenza in differential diagnosis especially for high-risk groups for influenza, and test and treat according to national guidance.
- In the temperate zones of the northern hemisphere, influenza activity although still low appeared to increase in some countries with detections of mainly influenza A(H3N2) viruses and in China B-Victoria lineage viruses.
- In North America, influenza virus detections of predominately A(H3N2) among the subtyped increased and hospitalizations are increasing but remains low overall. RSV activity decreased in the USA and Canada.
- In Europe, influenza activity continued to increase. Influenza A(H3N2) predominated.
- In East Asia, influenza activity continued on an increasing trend in China, while influenza illness indicators and activity remained low in the rest of the subregion. Influenza B-Victoria lineage viruses predominated.
- In the Caribbean and Central American countries, influenza A(H3N2) and B virus detections increased in some countries.
- In tropical South America, influenza A(H3N2) detections increased overall. Severe acute respiratory infection (SARI) levels were reported at extraordinary levels in Bolivia (Plurinational State).
- In tropical Africa, overall influenza activity continued on a decreasing trend, with both influenza A and B detected.
- In Southern Asia, influenza virus detections of predominately influenza A(H3N2) increased overall, although decreasing in a few countries.
- In South-East Asia, sporadic influenza detections were reported in the Philippines.
- In the temperate zones of the southern hemisphere, influenza activity remained low overall, although increased detections of influenza A(H3N2) were reported in temperate South America.
- National Influenza Centres (NICs) and other national influenza laboratories from 110 countries, areas or territories reported data to FluNet for the time period from 6 December 2021 to 26 December 2021* (data as of 2022-01-07 11:00:29 UTC). The WHO GISRS laboratories tested more than 522595 specimens during that time period. A total of 27153 were positive for influenza viruses, of which 19980 (73.6%) were typed as influenza A and 7173 (26.4%) as influenza B.
- Of the sub-typed influenza A viruses, 352 (4.4%) were influenza A(H1N1)pdm09 and 7625 (95.6%) were influenza A(H3N2). Of the characterized B viruses, 3 (~0%) belonged to the B-Yamagata lineage and 6819 (~100%) to the B-Victoria lineage.
