Influenza Update N° 463

Overview

22 January 2024, based on data up to 7 January 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 in integrated surveillance and report to RespiMART (FluNet and FluID) directly or via regional platforms. Clinicians should consider influenza in differential diagnosis, especially for high-risk groups for influenza, and test and treat according to national and WHO guidance. Under-reporting due to the end of the year holidays may affect the data and conclusions below.
• Globally, influenza detections decreased, although some countries in the Northern hemisphere continued to report increasing activity.
• In the countries of North America, influenza activity remained elevated, as expected for the time of year. Influenza A(H1N1)pdm09 viruses predominated among the detections.
• In Europe and Central Asia, influenza activity continued to increase above the 10% positivity epidemic threshold. The influenza season in the region began in week 51. Of thirty-six reporting countries, influenza activity was reported at very high intensity in one, high intensity in five, medium intensity in ten, low intensity in sixteen and below baseline in four, and geographic spread was widespread in twenty of thirty-six reporting countries. Influenza hospitalizations and intensive care unit (ICU) admissions increased sharply. Influenza A virus detections predominated among detections in primary and secondary care sentinel surveillance, with A(H1N1)pdm09 viruses predominant.
• In Northern Africa, detections of predominantly influenza A(H1N1)pdm09 continued to increase, with elevated and increasing activity reported in Algeria and Tunisia and elevated but decreasing detections of A(H1N1)pdm09 and B viruses in Egypt.
• In Eastern Asia, influenza activity remained elevated but appeared to decrease overall due to decreases in China and the Republic of Korea. Increasing activity was reported in Hong Kong SAR, China and in Mongolia.​  
• In Western Asia, influenza activity driven by all seasonal subtypes decreased overall.​ Increased detections of influenza A viruses were reported in Georgia, Lebanon and Türkiye.​ ​Decreased activity was reported in the countries of the Arabian Peninsula.
• In the Central American and Caribbean countries, influenza activity increased in the Caribbean and decreased in Central America. Influenza A(H1N1)pdm09 viruses were predominant in the Caribbean followed by influenza A(H3N2) viruses, while influenza A(H1N1)pdm09 was predominant in Central America, followed by B/Victoria.
• In tropical South America, influenza activity decreased with few detections of influenza A and B viruses reported in most countries
• In tropical Africa, influenza detections remained low in Western and Middle Africa and decreased in Eastern Africa. Influenza A(H3N2) viruses predominated.
• In Southern Asia, overall influenza activity decreased but remained elevated in some countries, with increasing proportions of influenza B and A(H3N2) in recent weeks. 
• In South-East Asia, influenza activity driven by all seasonal subtypes decreased but remained elevated, with influenza A(H3N2) predominant
• In the temperate zones of the southern hemisphere, indicators of influenza activity were reported at low levels or below the seasonal threshold in most reporting countries. 
• National Influenza Centres (NICs) and other national influenza laboratories from 112 countries, areas or territories reported data to FluNet for the time period from 25 December 2023 to 07 January 2024* (data as of 19/01/2024 08:19:15 AM UTC). The WHO GISRS laboratories tested more than 323 975 specimens during that time period. 67 212 were positive for influenza viruses, of which 56 603 (84.2%) were typed as influenza A and 10 609 (15.8%) as influenza B. Of the sub-typed influenza A viruses, 8163 (27.0%) were influenza A(H1N1)pdm09 and 22 045 (73.0%) were influenza A(H3N2). Of the type B viruses for which lineage was determined, all (9393) belonged to the B/Victoria lineage.

• Globally, SARS-CoV-2 positivity from sentinel surveillance remained around 8%. Positivity was highest in the South-East Asia Region, where it increased sharply to around 11%. A smaller increase to around 7% was reported in the Western Pacific Region. Positivity decreased to around 10% and 9% respectively in the Eastern Mediterranean Region and the Region of the Americas in the latest week, following increases in previous weeks. Positivity was stable around 5% in the African region and decreased to around 8% in the European Region. SARS-CoV-2 positivity from non-sentinel surveillance decreased to around 15% globally.
• In countries with RSV surveillance in place, RSV activity was stable or decreased in most reporting countries in Europe and remained stable in North America. In Israel, RSV activity continued to increase in both inpatient and outpatient settings. RSV activity was elevated in Egypt. Activity was low or decreasing elsewhere. 
• 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://www.who.int/publications/i/item/WHO-2019-nCoV-integrated_sentinel_surveillance-2022.1.
• National Influenza Centres (NICs) and other national influenza laboratories from 78 countries, areas or territories from six WHO regions (African Region: 11; Region of the Americas: 16; Eastern Mediterranean Region: 6; European Region: 35; South-East Asia Region: 5; Western Pacific Region: 5) reported to FluNet from sentinel surveillance sites for time period from 25 December 2023 to 07 January 2024* (data as of 19/01/2024 08:19:15 AM UTC). The WHO GISRS laboratories tested more than 28 081 sentinel specimens during that period and 2199 (7.83%) were positive for SARS-CoV-2. Additionally, more than 13 400 non-sentinel or undefined reporting source samples were tested in the same period and 3036 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.