2021-09-26-世界卫生组织-Influenza_Update_N°_403_11页_1mb

Influenza Update Summary

This update assesses global influenza activity based on data up to September 12, 2021. Interpretation should consider that the COVID-19 pandemic has influenced testing capacity, surveillance practices, and influenza transmission.

Global Trends

• Influenza activity remained lower than predicted for this season/year globally, despite increased testing in some areas.
• Activity is at "inter-seasonal levels" in the northern and southern hemispheres' temperate zones.
• Sporadic detections reported from various regions.

Virus Detection

• Both influenza A and B viruses were detected.
• WHO GISRS laboratories tested over 275,940 specimens (8,136 positive), with slightly more B than A viruses identified (57.1% B, 42.9% A).
• Among A viruses, 92.7% were H3N2 and 7.3% were H1N1pdm09.
• Among B viruses, 99.8% were Victoria lineage and 0.2% were Yamagata lineage.

By Region

• Temperate Zones (Northern Hemisphere): Below baseline activity reported overall. Activity low, predominant in Europe were A(H3N2) and B, while East Asia showed moderate B viruses.
• Temperate Zones (Southern Hemisphere): Activity at inter-seasonal levels. Oceania reported low activity; South Africa prevalent B/Victoria; South America no detections. RSV activity and COVID-19 decreased in South Africa.
• Tropical Zones:
  • Caribbean/Central Americas & Tropical South America: Mostly sporadic B detections, some A in specific countries. RSV activity generally higher/elevated reported.
  • Tropical Africa: Detections in various countries, lineages varied. RSV elevated in some areas; COVID-19 activity, sometimes linked to increased influenza rates.
  • Southern/Tropical Asia: Predominant activity reported in Southern Asia, mostly H3N2 and B/Victoria, but some declining trends in India and Nepal.

COVID-19 Impact & Next Steps

• The widespread non-pharmaceutical interventions for COVID-19 likely impacted influenza transmission.
• WHO encourages continued influenza surveillance, timely reporting, and agreed on recommendations for the 2021-2022 Southern Hemisphere vaccine composition, based partly on the limited e-consultation held.
• Some SARS-CoV-2 sentinel surveillance shows declining percent positivity, although activity remains elevated across many regions. Data inclusion is limited.