Influenza Update N° 442

Overview

03 April 2023, based on data up to 19 March 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 southern 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.
• Globally, influenza detections decreased steeply in January after a peak in late 2022. Detections in 2022 were predominantly influenza A(H3N2). Since the end of January 2023, activity increased again with an increased proportion of influenza A(H1N1)pdm09 and B virus detections, and detections appear to have decreased in the most recent week.
• In the countries of North America, most indicators of influenza activity were at levels typically observed towards the end of the season. Influenza A viruses predominated overall, with influenza A(H1N1)pdm09 accounting for the majority of subtyped influenza A viruses in the United States of America (USA), whereas influenza B viruses predominated in Canada.
• In Europe, overall influenza detections decreased and influenza positivity from sentinel sites was stable and remained above the epidemic threshold at the regional level. Out of 37 countries, 16 reported medium intensity with the remainder reporting low or below baseline intensity. Eighteen of 36 countries reported widespread activity. Overall, influenza B viruses predominated in both sentinel and non-sentinel surveillance as all subregions experienced a wave of influenza B activity after an initial influenza A wave. Influenza detections decreased or were stable in most countries except in Denmark, Iceland, Lithuania, Luxembourg and Germany where slight increases were reported.
• In Central Asia, influenza activity decreased. ​
• In Northern Africa, influenza detections were very low across reporting countries.
• In Western Asia, influenza activity continued to be reported in some countries with detections of all seasonal influenza subtypes.
• In East Asia, influenza activity of predominantly A(H1N1)pdm09 steeply increased in China but decreased in the other reporting countries.
• In the Caribbean and Central American countries, influenza activity of mainly influenza B/Victoria lineage viruses remained low in most reporting countries. Increases in influenza activity were reported in Belize, El Salvador and Guatemala where activity increased to moderate levels.
• In the tropical countries of South America, influenza remained low with all seasonal subtypes detected and influenza B viruses predominant. Slight increased trends in influenza activity and detections were reported in Bolivia (Plurinational State of) and Brazil.
• In tropical Africa, influenza activity increased in some countries of Western Africa while detections were low across reporting countries in Middle and Eastern Africa.
• In Southern Asia, influenza activity remained low with influenza A(H3N2) and B/Victoria lineage viruses predominant.
• In South-East Asia, influenza activity remained elevated with influenza B mainly detected in Malaysia and A(H3N2) in Singapore and Thailand.
• In the temperate zones of the southern hemisphere, influenza activity remained low.
• Globally, RSV activity was generally low or decreasing except in Australia, New Zealand and South Africa. RSV activity increased but remained below the seasonal threshold in parts of Australia and detections among hospitalized SARI patients increased in New Zealand. In South Africa, the RSV season started in week 6 of 2023 and the detection rate among children under five years of age in pneumonia surveillance has reached a moderate level. RSV remained elevated in Brazil and Mexico.
• National Influenza Centres (NICs) and other national influenza laboratories from 115 countries, areas or territories reported data to FluNet for the time period from 06 March 2023 to 19 March 2023* (data as of 3/31/2023 6:38:27 AM UTC). The WHO GISRS laboratories tested more than 349 552 specimens during that time period. 46 911 were positive for influenza viruses, of which 34 346 (73.22%) were typed as influenza A and 12 565 (26.78%) as influenza B. Of the sub-typed influenza A viruses, 20 264 (70.30%) were influenza A(H1N1)pdm09 and 8560 (29.70%) were influenza A(H3N2). Of the characterized B viruses, 100% (1479) belonged to the B/Victoria lineage.

• SARS-CoV-2 positivity from sentinel surveillance remained around 20% globally. Activity remained around 25% in the WHO Region of the Americas and around 15% in the Eastern Mediterranean region.  Activity remained around 10% in the other regions. SARS-CoV-2 positivity from non-sentinel surveillance was reported around 30% 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 81 countries, areas or territories reported data to FluNet for the time period from six WHO regions (African Region: 10; Region of the Americas: 19; Eastern Mediterranean Region: 5; European Region: 38; South-East Asia Region: 4; Western Pacific Region: 5) reported to FluNet from sentinel surveillance sites for time period from 06 March 2023 to 19 March 2023* (data as of 3/31/2023 6:38:27 AM UTC). The WHO GISRS laboratories tested more than 39 336 sentinel specimens during that time period and 7456 (18.95%) were positive for SARS-CoV-2. Additionally, more than 115 858 non-sentinel or undefined reporting source samples were tested in the same period and 32 305 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.