Influenza Update N° 462

Overview

08 January 2024, based on data up to 24 December 2023, except where otherwise noted

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 increased due to increases in the temperate Northern hemisphere, mainly in parts of Europe, Central Asia and North America.
• In the countries of North America, influenza activity continued to increase and was near expected levels for this time of year. Influenza hospitalizations have increased in recent weeks. Influenza A(H1N1)pdm09 viruses predominated among the detections.
• In Europe and Central Asia, as of the week ending 31 December 2023, influenza activity increased sharply overall above the 10% positivity epidemic threshold. Of 31 reporting countries, influenza activity was reported at very high intensity in one, high intensity in two, medium intensity in nine, low intensity in 14 and below baseline in the others, and geographic spread was widespread in 15 of 30 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 primary care sentinel surveillance and A(H3N2) viruses predominant in secondary care sentinel surveillance.
• In Northern Africa, detections of predominantly influenza A(H1N1)pdm09 continued to increase in Algeria and detections of A(H1N1)pdm09 and B viruses decreased in Egypt.
• In East Asia, influenza activity remained elevated mainly due to activity in China and the Republic of Korea.
• In Western Asia, influenza activity continued to be reported in some countries of the Arabian Peninsula and remained low in other reporting countries except for Lebanon that reported increased influenza A(H1N1)pdm09 virus detections.
• In the Central American and Caribbean countries, influenza activity remained moderate in the Caribbean with detections of predominantly influenza A(H1N1)pdm09 and low in Central America with detections of predominantly B/Victoria lineage viruses.
• In tropical South America, influenza activity remained low.
• In tropical Africa, influenza detections remained low in Western Africa and decreased in Eastern Africa. Influenza A(H3N2) viruses predominated. A few detections were reported in Middle Africa.
• In Southern Asia, influenza activity was stable with predominantly influenza A viruses, of which similar numbers of A(H1N1)pdm09 and A(H3N2) detections were reported overall.
• In South-East Asia, influenza activity driven by all seasonal subtypes remained stable overall.
• In the temperate zones of the southern hemisphere, indicators of influenza activity were reported at low levels or the below seasonal threshold in most reporting countries.
• National Influenza Centres (NICs) and other national influenza laboratories from 117 countries, areas or territories reported data to FluNet for the time period from 11 to 24 December 2023 (data as of 05/01/2024 07:00:39 PM UTC). The WHO GISRS laboratories tested more than 585 784 specimens during that time period. 100 299 were positive for influenza viruses, of which 86 897 (86.6%) were typed as influenza A and 13 402 (13.4%) as influenza B. Of the sub-typed influenza A viruses, 11 109 (27.3%) were influenza A(H1N1)pdm09 and 29 546 (72.7%) were influenza A(H3N2). Of the type B viruses for which lineage was determined, all (7053) belonged to the B/Victoria lineage. 

• Globally, SARS-CoV-2 positivity from sentinel surveillance remained around 7%. Positivity was highest in the European Region, where it was around 16%. Positivity was stable around or below 5% in the other regions. SARS-CoV-2 positivity from non-sentinel surveillance was around 20% globally.
• In countries with RSV surveillance in place, RSV activity was stable or decreased in North America and in most reporting countries in Europe. Activity remained elevated in Central America and was generally 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://covid.comesa.int/publications/i/item/WHO-2019-nCoV-integrated_sentinel_surveillance-2022.1.
• NICs and other national influenza laboratories from 79 countries, areas or territories from six WHO regions (African Region: 11; Region of the Americas: 15; Eastern Mediterranean Region: 5; European Region: 35; South-East Asia Region: 7; Western Pacific Region: 6) reported to FluNet from sentinel surveillance sites for time period from 11 to 24 December 2023 (data as of 05/01/2024 07:00:39 PM UTC). The WHO GISRS laboratories tested more than 31 320 sentinel specimens during that period and 2522 (8.1%) were positive for SARS-CoV-2. Additionally, more than 22 805 non-sentinel or undefined reporting source samples were tested in the same period and 4186 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) hosted by WHO RespiMART platform and influenza and other respiratory virus reports from WHO Regional Offices and Member States. During the COVID-19 pandemic, FluNet has also been receiving updates on testing of samples obtained from routine influenza surveillance systems for SARS-CoV-2. 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.