Weekly updates, Influenza Epidemiological Week 15 (21 April 2023)

North America: Influenza activity has been on the rise, with Mexico reporting an increase in activity. Influenza B (Victoria lineage in cases where it has been determined) and influenza A (H1N1)pdm09 have been circulating concurrently. Respiratory syncytial virus (RSV) activity has remained low, while SARS-CoV-2 activity has remained at moderate levels. 

Caribbean: An increase in influenza activity has been detected. Influenza B Victoria lineage has predominantly circulated. The countries where increases in activity have been detected are Belize and Jamaica. RSV and SARS-CoV-2 activity has remained low. 

Central America: Influenza activity has remained stable, with predominance of influenza A (H1N1)pdm09 and influenza B Victoria, and to a lesser extent, influenza A (H3N2) circulation. The countries with the highest activity have been Costa Rica, El Salvador, and Guatemala. RSV and SARS-CoV-2 activity has remained low. 

Andean Countries: Influenza activity has increased, especially in Bolivia. Circulation has also been detected in Ecuador and Peru, but to a lesser extent. Influenza A (H1N1)pdm09 has predominated, although some detections of influenza A (H3N2) and influenza B Victoria have also been reported. RSV activity remains low, and SARS-CoV-2 activity remains at intermediate levels. 

Brazil and Southern Cone: Influenza activity has increased, especially in Chile and Paraguay, with circulation of influenza A (H1N1)pdm09 and influenza B Victoria. RSV and SARS-CoV-2 activity remains stable at low levels. 

Global: 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 decreased. 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. 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, most were influenza A(H1N1)pdm09. Influenza detections decreased or were stable in most countries except Lithuania and Norway, where slight increases were reported. In Central Asia, sporadic influenza detections were reported in Kazakhstan (influenza A(H1N1)pdm09) and Tajikistan. In Northern Africa, influenza detections were very low. In Western Asia, influenza activity 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, the Hong Kong Special Administrative Region (SAR), China, and the Republic of Korea. 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 Australia. RSV activity was generally low or decreasing globally except in Australia, New Zealand, and South Africa. 

SARS-CoV-2 positivity from sentinel surveillance decreased from around 20% to 12% globally. Activity decreased slightly to about 20% in the Americas but increased to just below 20% in the Eastern Mediterranean Region. Activity remained around or below 10% in the other regions. SARS-CoV-2 positivity from non-sentinel surveillance was reported at around 23% globally. 

Avian Influenza: A summary of the avian influenza situation in the region, case management and recommendations are available at Epidemiological alerts and updates | PAHO/WHO | Pan American Health Organization (paho.org)