Influenza Update N° 404

Overview

11 October 2021, based on data up to 26 September 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 southern hemisphere, influenza activity remained at inter-seasonal levels, although a slight increase in influenza A and B detections was reported from South Africa.
• In the temperate zones of the northern hemisphere, influenza activity remained at inter-seasonal levels. Influenza B predominated among detections 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, sporadic influenza B detections were reported in the Philippines.
• Worldwide, influenza B(Victoria) viruses predominated.
• National Influenza Centres (NICs) and other national influenza laboratories from 88 countries, areas or territories reported data to FluNet for the time period from 13 September 2021 to 26 September 2021 (data as of 2021-10-08 06:58:25 UTC).The WHO GISRS laboratories tested more than 242316 specimens for influenza during that time period. 2022 were positive for influenza viruses, of which 640 (31.7%) were typed as influenza A and 1382 (68.3%) as influenza B. Of the sub-typed influenza A viruses, 88 (15.8%) were influenza A(H1N1)pdm09 and 470 (84.2%) were influenza A(H3N2). Of the characterized B viruses, 100% (1213) belonged 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 appeared to decrease, returning to levels last observed in mid-2021. Activity was low in the WHO African and Western Pacific regions at under 5% positivity. Activity decreased in the WHO region of the Americas, but remained at elevated levels above 20%. Activity increased within the WHO Eastern Mediterranean, European and South East Asian regions and remained at elevated levels between 13 and 33%. Overall positivity from non-sentinel sites continued to decrease and remained under 10% for most regions. 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 35 countries, areas or territories from six WHO regions (African Region: 1;  Region of the Americas: 13;  Eastern Mediterranean Region: 3;  European Region: 11;  South-East Asia Region: 3;  Western Pacific Region: 4 ) reported to FluNet from sentinel surveillance sites for time period from 13 Sep 2021 to 26 Sep 2021 (data as of 2021-10-08 06:58:25 UTC). The WHO GISRS laboratories tested more than 46 657 sentinel specimens during that time period and 13 286 (28.5%) were positive for SARS-CoV-2. Additionally, more than 1 384 796 non-sentinel or undefined reporting source samples were tested in the same period and 105 767 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.