Influenza Update N° 443

Overview

17 April 2023, based on data up to 02 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 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). After the end of January 2023, activity increased again with a higher proportion of influenza A(H1N1)pdm09 and B virus detections until a peak around week 10, after which detections have decreased.
• 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 in the United States of America (USA), with influenza A(H1N1)pdm09 accounting for the majority of subtyped viruses, whereas influenza B viruses predominated in Canada.
• In Europe, overall influenza detections decreased and influenza positivity from sentinel sites decreased to 16% but remained above the epidemic threshold at the regional level. Out of 41 countries, 13 reported moderate intensity, with the remainder reporting low or below baseline intensity. Out of 40 countries, 20 continued to report 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. Of the few influenza A viruses detected, the majority were influenza A(H1N1)pdm09. Influenza detections decreased or were stable in most countries except in Lithuania and Norway where very slight increases were reported.
• In Central Asia, sporadic influenza detections were reported in Kazakhstan (influenza A(H1N1)pdm09) and Tajikistan (influenza B).
• In Northern Africa, influenza detections were very low.
• In Western Asia, influenza activity overall decreased but continued to be reported in some countries with detections of all seasonal influenza subtypes.
• In East Asia, influenza activity continued to be driven predominantly by A(H1N1)pdm09 detections in China, which appeared to reach a peak and decrease slightly. Slight increases in some indicators of influenza activity were reported in China, Hong Kong Special Administrative Region (SAR), China and the Republic of Korea.
• In the Caribbean and Central American countries, influenza activity of mainly influenza B/Victoria lineage viruses was low, although increases in influenza activity were reported in Belize and Guatemala where activity was close to the moderate threshold.
• In the tropical countries of South America, influenza remained low with all seasonal subtypes detected and influenza B viruses predominant. Increasing trends in influenza activity and detections were reported in Brazil and Peru however activity remained low. In Bolivia (Plurinational State of), SARI activity remained high and RSV activity increased.
• 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 predominating.
• In South-East Asia, influenza activity remained elevated mainly due to influenza B detections in Malaysia and influenza A(H3N2) in Singapore.
• In the temperate zones of the southern hemisphere, influenza activity remained low however influenza activity increased slightly in Chile and Australia.
• Globally, RSV activity was generally low or decreasing except in Australia, New Zealand, South Africa and a few countries in the Region of the Americas. 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 detection rate among children under five years of age in pneumonia surveillance reached a very high level. RSV remained elevated in Guatemala and Mexico and increased in Bolivia (Plurinational State of).
• National Influenza Centres (NICs) and other national influenza laboratories from 120 countries, areas or territories reported data to FluNet for the time period from 20 March 2023 to 02 April 2023* (data as of 4/14/2023 8:04:40 AM UTC). The WHO GISRS laboratories tested more than 381 110 specimens during that time period. 40 010 were positive for influenza viruses, of which 30 057 (75.12%) were typed as influenza A and 9953 (24.88%) as influenza B. Of the sub-typed influenza A viruses, 18 779 (70.42%) were influenza A(H1N1)pdm09 and 7890 (29.58%) were influenza A(H3N2). Of the characterized B viruses, 100% (1163) belonged to the B/Victoria lineage.

• SARS-CoV-2 positivity from sentinel surveillance decreased from around 20% to around 12% globally. Activity decreased slightly to around 20% in the Region of the Americas but increased in the Eastern Mediterranean to just below 20%. Activity remained around or below 10% in the other regions.  SARS-CoV-2 positivity from non-sentinel surveillance was reported around 23% 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 83 countries, areas or territories from six WHO regions (African Region: 14; Region of the Americas: 18; Eastern Mediterranean Region: 5; European Region: 37; South-East Asia Region: 4; Western Pacific Region: 5) reported to FluNet from sentinel surveillance sites for time period from 20 March 2023 to 02 April 2023* (data as of 4/14/2023 8:04:40 AM UTC). The WHO GISRS laboratories tested more than 33 718 sentinel specimens during that time period and 4766 (14.13%) were positive for SARS-CoV-2. Additionally, more than 86 900 non-sentinel or undefined reporting source samples were tested in the same period and 19 606 were positive for SARS-CoV-2. Further details are included at the end of this update.

Source of data

______________________________________________________________________________________________

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.