WHO releases new data on worldwide influenza activity

By Neha MathurReviewed by Aimee MolineuxNov 17 2022

The World Health Organization (WHO) regional offices and member states, in collaboration with its Global Influenza Surveillance and Response System (GISRS), collate and report data on influenza activity worldwide every two weeks.

National Influenza Centres (NICs) and other national influenza laboratories from 105 countries, areas, or territories report data to FluNet.

The latest report updated up to 30 October 2022 has data categorized by influenza transmission zones, i.e., countries/regions with similar influenza transmission patterns.

In addition, it covers epidemiological and virological FluNet data for the period between 17 October 2022 and 30 October 2022. During this time, the WHO GISRS laboratories tested over 229,940 specimens.

Key highlights

Influenza activity increased globally, and especially influenza A(H3N2) virus subtype became predominant. Of 229,940 specimens tested, 15,723 were positive for influenza viruses. The share of influenza A and influenza B viruses was 14,589 (92.8%) and 1134 (7.2%). While all characterized B viruses belonged to the B/Victoria lineage, 1424 (21.2%) and 5284 (78.8%) of 14,589 influenza A viruses were H1N1 and H3N2, respectively.

At the hemispherical level, while the upward trend in influenza activity continued in the northern hemisphere, it plateaued in the southern hemisphere. Based on this observation, the WHO recommended that Northern hemisphere countries, including the United States and Canada, step up their influenza vaccination campaign to prevent hospitalizations and deaths. More importantly, medical doctors should screen or test people for influenza and treat them per national guidance.

Despite a sharp increase in COVID-19 activity in the WHO Region of the Americas and a slight increase in South-East Asia and Western Pacific Regions, sentinel surveillance results showed it remained under 10% following a long-term downward trend beginning in mid of 2022.

Thus, the WHO encouraged stepping up integrated surveillance for influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in countries harbored in the northern hemisphere. They specifically focused on countries that have received the multiplex influenza and SARS-CoV-2 reagent kits from GISRS. The WHO even published revised interim guidance for these countries emphasizing the urgent need to report epidemiological and laboratory information on time to their regional and global platforms.

Temperate-zone countries (Northern Hemisphere)

In countries of the temperate zone of the Northern hemisphere, such as the US and Canada, influenza-like illness (ILI) and respiratory syncytial virus (RSV) activity increased above the seasonal average for this time of year, with influenza A(H3N2) virus being predominant. SARS-CoV-2 continues to be the causal agent behind above-the-epidemic threshold mortality in the USA.

Influenza A(H3N2) predominated in European countries, with the highest ILI activity reported in South West Europe (3.62% positivity). Portugal, followed by Germany and Spain, reported an increasing trend in ILI activity. RSV activity was the highest in France and continuously increasing. Likewise, excess mortality across most age groups continued to surge in European countries. The Central (e.g., Kazakhstan) and West Asian countries, like Saudi Arabia, reported high/elevated ILI activity, with B-lineage influenza viruses predominating in Kazakhstan. On the contrary, in East Asia, influenza A(H3N2) activity remained stable at intermediate levels.

Temperate zone countries (Southern Hemisphere)

The overall ILI activity appeared to decrease in this reporting period, except in South America, where ILI activity increased in several countries, such as Argentina, Chile, and Uruguay. In Chile and Uruguay, influenza A(H3N2) viruses predominated, while influenza B and influenza A(H1N1) were predominant in Argentina. Across all Pacific Islands, including New Zealand, ILI activity remained low except in a few countries. Likewise, in Australia, ILI activity remained minimal, though testing detected influenza A(H1N1), influenza A(H3N2), and some B viruses.

Tropical countries

The tropical countries of South America and Africa had low ILI activity during the study reported period. Notably, RSV activity increased only in Brazil. In Puerto Rico and Guatemala, parts of the Caribbean, and Central America, ILI activity was above the average for this time of year and the seasonal threshold.