Influenza Update N° 406

Overview

8 November 2021, based on data up to 24 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 interseasonal 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 A and B virus detections, as well as elevated 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 and some influenza B viruses were reported. Previously increased activity in West African appeared to be decreasing.
• In Southern Asia, the number of influenza virus detections reported was in a similar range to previous seasons with detections of influenza A and B viruses. Previously elevated levels of severe acute respiratory infections (SARI) in some countries appeared to decrease.
• In South-East Asia, few detections of influenza A(H3N2) and influenza B were reported from Myanmar.
• In the temperate zones of the southern hemisphere, influenza activity remained at interseasonal levels. Elevated RSV activity continued to be reported in some countries.
• Globally, among influenza detections, influenza B viruses predominated.
  
• National Influenza Centres (NICs) and other national influenza laboratories from 102 countries, areas or territories reported data to FluNet for the time period from 11 October 2021 to 24 October 2021 (data as of 2021-11-05 10:02:16 UTC).The WHO GISRS laboratories tested more than 307999 specimens during that time period. 2199 were positive for influenza viruses, of which 875 (39.8%) were typed as influenza A and 1324 (60.2%) as influenza B. Of the sub-typed influenza A viruses, 186 (36.2%) were influenza A(H1N1)pdm09 and 328 (63.8%) were influenza A(H3N2). Of the characterized B viruses, 1 (0.1%) belonged to the B-Yamagata lineage and 1176 (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. Activity indicated positivity under 10% for all regions except the WHO region of the Americas. However, activity continued to decrease in this region and positivity was 16%. 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 nonsentinel sites, activity remained elevated and above 20%.
• NICs and other national influenza laboratories from 42 countries, areas or territories from six WHO regions (African Region: 1; Region of the Americas: 13; Eastern Mediterranean Region: 3; European Region: 17; South-East Asia Region: 4; Western Pacific Region: 4) reported to FluNet from sentinel surveillance sites for time period from 11 Oct 2021 to 24 Oct 2021 (data as of 2021-11-05 10:02:16 UTC). The WHO GISRS laboratories tested more than 59 166 sentinel specimens during that time period and 10 523 (17.8%) were positive for SARS-CoV-2. Additionally, more than 1400670 non-sentinel or undefined reporting source samples were tested in the same period and 105925 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.