Influenza Update N° 405

Overview

25 October 2021, based on data up to 10 October 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. The 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, despite continued or even increased testing for influenza in some countries, influenza activity remained at lower levels than expected for this time of the year. 
• In the temperate zones of the northern hemisphere, influenza activity remained at inter-seasonal levels. Both influenza A and B were detected, and respiratory syncytial virus (RSV) was increased and higher than in previous years in some countries.
• In the Caribbean and Central American countries, sporadic influenza B virus detections and RSV activity were reported in some countries 
• In tropical South America, no influenza detections were reported, however RSV activity remained elevated in some countries.  
• In tropical Africa, a few influenza detections of predominately influenza A were reported in some countries in Western, Middle and Eastern Africa.
• In Southern Asia, influenza detections of predominately influenza B continued to be reported across reporting countries. 
• In South-East Asia, no influenza detection was reported.
• In the temperate zones of the southern hemisphere, influenza activity remained at inter-seasonal levels. Elevated influenza-like illness (ILI) and RSV activity was reported in some countries.
• Worldwide, influenza B/Victoria lineage viruses predominated.
• National Influenza Centres (NICs) and other national influenza laboratories from 95 countries, areas or territories reported data to FluNet for the time period from 27 September 2021 to 10 October 2021 (data as of 2021-10-22 07:48:51 UTC). The WHO GISRS laboratories tested more than 240 512 specimens during that time period. 2219 were positive for influenza viruses, of which 763 (34.4%) were typed as influenza A and 1456 (65.6%) as influenza B. Of the sub-typed influenza A viruses, 169 (34%) were influenza A(H1N1)pdm09 and 328 (66%) were influenza A(H3N2). Of the characterized B viruses, 2 (0.1%) belonged to the B-Yamagata lineage and 1339 (99.9%) to the B-Victoria lineage.

• During the COVID-19 pandemic, WHO encourages countries, especially those that have received the multiplex influenza and SARS-CoV-2 reagent kits from GISRS, to continue routine influenza surveillance, test samples from influenza surveillance sites for influenza and SARS-CoV-2 viruses where resources are available and report epidemiological and laboratory information in a timely manner to established regional and global platforms (see the guidance here: https://apps.who.int/iris/rest/bitstreams/1316069/retrieve).
• At the global level, SARS-CoV-2 percent positivity from sentinel surveillance continued to decrease, returning to levels last observed in mid-2021. Activity was low in the WHO African and, South-East Asian and Western Pacific regions at under 5% positivity. Activity decreased in the WHO region of the Americas, Eastern Mediterranean and European regions but remained at elevated levels between 10% and 30%. Overall positivity from non-sentinel sites continued to decrease, reaching a low of just under 7%. While activity showed a decreasing trend in the WHO South-East Asian region non-sentinel sites, activity remained elevated and above 40%.
• NICs and other national influenza laboratories from 39 countries, areas or territories from six WHO regions (African Region: 1;  Region of the Americas: 13;  Eastern Mediterranean Region: 3;  European Region: 13;  South-East Asia Region: 4;  Western Pacific Region: 5 ) reported to FluNet from sentinel surveillance sites for time period from 27 Sep 2021 to 10 Oct 2021 (data as of 2021-10-22 07:48:51 UTC). The WHO GISRS laboratories tested more than 66 572 sentinel specimens during that time period and 15 438 (23.2%) were positive for SARS-CoV-2. Additionally, approximately 1.5 million non-sentinel or undefined reporting source samples were tested in the same period and 110 981 were positive for SARS-CoV-2. Further details are included at the end of this update. 

Source of data

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The Global Influenza Programme monitors influenza activity worldwide and publishes an update every two weeks. The updates are based on available epidemiological and virological data sources, including FluNet (reported by the WHO Global Influenza Surveillance and Response System), FluID (epidemiological data reported by national focal points) and influenza reports from WHO Regional Offices and Member States. Completeness can vary among updates due to availability and quality of data available at the time when the update is developed.

^*It includes data only from countries reporting on positive and negative influenza specimens.