Influenza Update N° 445

Overview

15 May 2023, based on data up to 30 April 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 RespiMART (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 and WHO guidance.
• Globally, influenza detections decreased further due to a decline in detections in the northern hemisphere, while some countries in the southern hemisphere reported an increase in influenza detections in recent weeks.
• In the countries of North America, most indicators of influenza activity were at levels typically observed between influenza seasons. Influenza B viruses predominated in Canada and, in the most recent week, in the United States of America (USA).
• In Europe, overall influenza detections decreased and influenza positivity from sentinel sites decreased below the epidemic threshold of 10% at the regional level. 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. Of the few influenza A viruses detected, the majority were influenza A(H1N1)pdm09. Influenza detections were low in all reporting countries.
• In Central Asia, no influenza detections were reported this period despite continued testing.).
• In Northern Africa, no influenza detections were reported.
• In Western Asia, influenza activity remained low overall with detections of all seasonal influenza subtypes.
• In East Asia, influenza activity decreased overall, although detections of mainly influenza A(H1N1)pdm09 continued to increase in Hong Kong Special Administrative Region (SAR), China. A slight increase of influenza detections was reported in the Republic of Korea.
• In the Caribbean and Central American countries, influenza activity of mainly influenza B/Victoria lineage viruses was low or below baseline in most countries, although increases in influenza activity were reported in a few countries.
• In the tropical countries of South America, influenza activity decreased overall during this reporting period although positivity increased to extraordinary level in Bolivia (Plurinational State of).
• In tropical Africa, influenza detections were low in reporting countries. Influenza A virus detections outnumbered B virus detections.
• In Southern Asia, influenza activity remained low with influenza B viruses predominant followed by A(H3N2) viruses. Influenza activity was low in reporting countries.
• In South-East Asia, influenza activity decreased overall, reflecting a decrease in detections in Malaysia. Influenza A(H3N2) viruses predominated overall. Singapore continued to report elevated detections of predominantly A(H3N2) viruses.
• In the temperate zones of the southern hemisphere, influenza activity remained low, however influenza activity increased slightly in Australia and Chile and in pneumonia surveillance in South Africa. Influenza A viruses were predominant and among the subtyped viruses and influenza A(H1N1)pdm09 predominated in these countries.
• Globally, RSV activity was generally low except in Australia and a few countries in the Region of the Americas. RSV activity decreased but remained elevated in parts of Australia. In South Africa, the RSV detection rate among children under five years of age in pneumonia surveillance decreased from a moderate to a low level. RSV remained elevated in Guatemala and increased in several countries in tropical and temperate South America.
• National Influenza Centres (NICs) and other national influenza laboratories from 111 countries, areas or territories reported data to FluNet for the time period from 17 April 2023 to 30 April 2023* (data as of 12/05/2023 7:56:00 AM UTC). The WHO GISRS laboratories tested more than 266 317 specimens during that time period. 18 330 were positive for influenza viruses, of which 14 209 (77.52%) were typed as influenza A and 4 121 (22.48%) as influenza B. Of the subtyped influenza A viruses, 8816 (69.58%) were influenza A(H1N1)pdm09 and 3854 (30.42%) were influenza A(H3N2). Of the type B viruses for which lineage was determined, all 587(100%) belonged to the B/Victoria lineage. 

• SARS-CoV-2 positivity from sentinel surveillance increased to 17% globally. Activity increased above 20% in the Eastern Mediterranean and Western Pacific regions and remained around 17% and 12% in the Region of the Americas and the European Region, respectively. Activity was around or below 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 77 countries, areas or territories from six WHO regions (African Region: 12; Region of the Americas: 17; Eastern Mediterranean Region: 4; European Region: 36; South-East Asia Region: 4; Western Pacific Region: 4) reported to FluNet from sentinel surveillance sites for time period from 17 April 2023 to 30 April 2023* (data as of 12/05/2023 7:56:00 AM UTC). The WHO GISRS laboratories tested more than 44 540 sentinel specimens during that time period and 6 835 (15.35%) were positive for SARS‑CoV-2. Additionally, more than 69 459 non-sentinel or undefined reporting source samples were tested in the same period and 16 706 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.