Influenza Update N° 439

Overview

20 February 2023, based on data up to 05 February 2023

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)

• Countries are recommended to monitor the relative co-circulation of influenza and SARS-CoV-2 viruses and report to FluNet and FLUID directly or via regional platforms. They are encouraged to enhance integrated surveillance and in northern hemisphere countries step-up their influenza vaccination campaign to prevent severe disease and hospitalizations associated with influenza. Clinicians should consider influenza in differential diagnosis, especially for high-risk groups for influenza, and test and treat according to national guidance. Because of changes in surveillance of respiratory viruses during the COVID-19 pandemic, comparisons of current data with that from previous seasons should be interpreted with caution.
• Globally, influenza activity was decreased compared to the peak in late 2022. Influenza A viruses predominated with a slightly larger proportion of A(H1N1)pdm09 viruses detected among the subtyped influenza A viruses. The proportion of influenza B virus detections increased during this reporting period.
• In the countries of North America, most indicators of influenza activity decreased to levels similar or below levels typically observed towards the end of the season. Influenza A viruses predominated and influenza A(H3N2) accounted for the majority of subtyped influenza A viruses in the United States of America (USA), whereas A(H1N1)pdm09 accounted for the majority of subtyped influenza A viruses in Canada.
• In Europe, overall influenza detections remained stable and influenza positivity from sentinel sites increased slightly and remained above the epidemic threshold at the regional level. Half of the countries reported high or moderate intensity, and most reported widespread activity. Overall, influenza A viruses predominated with A(H1N1)pdm09 accounting for the majority of subtyped influenza viruses from primary care sentinel sites but with regional differences. The proportion of influenza B viruses increased in recent weeks. Other indicators of influenza activity decreased in most countries while a few countries reported increases. 
• In Central Asia, influenza activity decreased overall. ​
• In Northern Africa, activity remained elevated with continued detections of all seasonal influenza subtypes reported in Morocco and Tunisia.
• In Western Asia, influenza activity decreased overall with all seasonal influenza subtypes detected, although increased activity continued to be reported in some countries. 
• In East Asia, influenza activity remained low overall although detections of all seasonal influenza subtypes increased in Mongolia in recent weeks.  ​
• In the Caribbean and Central American countries, influenza activity of influenza A(H3N2) and B viruses continued to decrease due to decreased detections reported by Mexico.
• In the tropical countries of South America, influenza remained low with all seasonal subtypes co-circulating.
• In tropical Africa, influenza activity was highest in eastern Africa but remained low overall with detections of all seasonal influenza subtypes reported.
• In Southern Asia, influenza activity remained low with all seasonal influenza subtypes detected.
• In South-East Asia, detections of predominantly influenza B viruses remained elevated due to continued detections reported in Malaysia.
• In the temperate zones of the southern hemisphere, influenza activity remained at inter-seasonal levels. 
• National Influenza Centres (NICs) and other national influenza laboratories from 124 countries, areas or territories reported data to FluNet for the time period from 23 January 2023 to 05 February 2023* (data as of 2023-02-17 08:06:54 UTC). The WHO GISRS laboratories tested more than 435 112 specimens during that time period. 27 978 were positive for influenza viruses, of which 19 219 (68.7%) were typed as influenza A and 8759 (31.3%) as influenza B. Of the sub-typed influenza A viruses, 3040 (57.9%) were influenza A(H1N1)pdm09 and 2211 (42.1%) were influenza A(H3N2). Of the characterized B viruses (900), 100% belonged to the B/Victoria lineage.

• SARS-CoV-2 positivity from sentinel surveillance remained at 20% globally. Activity was reported just below 30% in the WHO Region of the Americas, just above 20% in the Western Pacific Region and remained under 10% in the other regions. SARS-CoV-2 positivity from non-sentinel surveillance was reported around 25% globally. 
• 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 conduct integrated surveillance of influenza and SARS-CoV-2 and report epidemiological and laboratory information in a timely manner to established regional and global platforms. The guidance can be found here: https://covid.comesa.int/publications/i/item/WHO-2019-nCoV-integrated_sentinel_surveillance-2022.1.
• National Influenza Centres (NICs) and other national influenza laboratories from 75 countries, areas or territories from six WHO regions (African Region: 11;  Region of the Americas: 18;  Eastern Mediterranean Region: 4;  European Region: 33;  South-East Asia Region: 4;  Western Pacific Region: 5) reported to FluNet from sentinel surveillance sites for time period from 23 January 2023 to 05 February 2023* (data as of 2023-02-17 08:06:54 UTC). The WHO GISRS laboratories tested more than 44 821 sentinel specimens during that time period and 9242 (20.6%) were positive for SARS-CoV-2. Additionally, more than 159 983 non-sentinel or undefined reporting source samples were tested in the same period and 39 784 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.