Influenza Update N° 438

Overview

06 February 2023, based on data up to 22 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)

• enhance 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 decreased. Influenza A viruses predominated with a slightly larger proportion of A(H1N1)pdm09 viruses detected among the subtyped influenza A viruses during this reporting period.
• In the countries of North America, most indicators of influenza activity decreased to levels similar or below levels typically observed this time of year. Influenza A(H3N2) was the predominant virus detected in the United States of America whereas A(H1N1)pdm09 and A(H3N2) co-circulated in Canada in the most recent week.
• In Europe, overall influenza activity continued to decrease but influenza positivity from sentinel sites remained above the epidemic threshold at the regional level. 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. Many countries reported high or moderate intensity, and most reported widespread activity. Other indicators of influenza activity decreased in most countries while a few countries reported increases. 
• In Central Asia, influenza activity decreased overall but remained somewhat elevated, with influenza A(H1N1)pdm09 viruses predominant. ​
• In Northern Africa, influenza activity continued to decrease, with all seasonal influenza subtypes detected.
• In Western Asia, influenza activity decreased overall with all seasonal influenza subtypes detected, though increased activity was reported in some countries. 
• In East Asia, influenza activity of predominantly influenza A(H3N2) viruses remained low overall though detections continued to be reported at elevated levels in Mongolia and the Republic of Korea.  ​
• In the Caribbean and Central American countries, influenza activity of predominantly influenza A(H3N2) viruses was low overall.
• 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 slightly increased in this reporting period with all seasonal influenza subtypes detected in similar proportions.
• In South-East Asia, detections of predominantly influenza B remained elevated due to continued detections reported in Malaysia.
• In the temperate zones of the southern hemisphere, influenza activity remained at inter-seasonal level. 
• National Influenza Centres (NICs) and other national influenza laboratories from 127 countries, areas or territories reported data to FluNet for the time period from 09 January 2023 to 22 January 2023 * (data as of 2023-02-03 08:09:25 UTC). The WHO GISRS laboratories tested more than 367 930 specimens during that time period. 30 044 were positive for influenza viruses, of which 24878 (82.8%) were typed as influenza A and 5166 (17.2%) as influenza B. Of the sub-typed influenza A viruses, 4509 (58.6%) were influenza A(H1N1)pdm09 and 3192 (41.4%) were influenza A(H3N2). Of the characterized B viruses (592), 100% belonged to the B-Victoria lineage.

• SARS-CoV-2 positivity from sentinel surveillance remained above 20% globally. Activity was reported just below 30% in the WHO Region of the Americas and remained under 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://www.who.int/publications/i/item/WHO-2019-nCoV-integrated_sentinel_surveillance-2022.1.
• National Influenza Centres (NICs) and other national influenza laboratories from 74 countries, areas or territories from six WHO regions (African Region: 9;  Region of the Americas: 18;  Eastern Mediterranean Region: 6;  European Region: 34;  South-East Asia Region: 3;  Western Pacific Region: 4 ) reported to FluNet from sentinel surveillance sites for time period from 09 Jan 2023 to 22 Jan 2023* (data as of 2023-02-03 08:09:24 UTC). The WHO GISRS laboratories tested more than 48 012 sentinel specimens during that time period and 10 741 (22.4%) were positive for SARS-CoV-2. Additionally, more than 180 712 non-sentinel or undefined reporting source samples were tested in the same period and 55 318 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.