For 15 years, the WHO Working Group on Surveillance of Antiviral Susceptibility of Influenza Viruses (AVWG) has helped WHO answer a critical question for patient care and pandemic preparedness: do antiviral medicines used to treat influenza remain effective?
Through its surveillance activities, technical guidance, risk assessments, reference materials and laboratory tools, the AVWG supports WHO, the WHO Global Influenza Surveillance and Response System (GISRS) laboratories and public health decision-makers in monitoring and responding to emerging antiviral resistance.
Coordinated by the WHO Global Influenza Programme, AVWG is composed of experts from the WHO collaborating centres (CCs) on influenza, National Influenza Centres (NICs) and partner institutions, including the GISAID Data Science Initiative and OFFLU, the Network of Expertise on Animal Influenza of the World Organisation for Animal Health (WOAH) and the Food and Agriculture Organization of the United Nations (FAO).
Resistance remains low
At its 15th annual meeting in Hong Kong Special Administrative Region, China, on 10–12 June 2026, the AVWG reviewed global surveillance data and assessed antiviral susceptibility of contemporary viruses. The vast majority of seasonal and zoonotic influenza viruses tested remained susceptible to neuraminidase inhibitors (NAIs) and the polymerase inhibitor, baloxavir marboxil.
The H275Y neuraminidase (NA) substitution remains the primary marker associated with reduced inhibition by NA inhibitors (NAIs) oseltamivir and peramivir in A(H1N1)pdm09 influenza viruses and is typically detected following antiviral treatment in individual patients. In recent years, the global frequency of seasonal influenza A and B viruses circulated between 2020 to 2023 that showed reduced inhibition by NAIs or reduced susceptibility to baloxavir has remained low (<1%) (Hussain et al., Antiviral Research 2025). Most influenza viruses with markers of reduced inhibition by NAIs or reduced susceptibility to baloxavir were detected in patients who had previously received antiviral treatment. There was no evidence of sustained human-to-human onward transmission of these influenza viruses.
Detecting emerging threats
Through its work on antiviral susceptibility, the AVWG identifies and assesses genetic changes that may affect how influenza viruses respond to antiviral medicines.
A key function of AVWG is the regular update of reference tables of amino acid substitutions and their effect on antiviral susceptibility. These tables help laboratories and experts interpret genetic changes detected through surveillance and assess their potential public health significance. In 2026, the working group updated the tables with clearer guidance to support consistent interpretation among users of these tables, including the GISRS network laboratories.
The AVWG also develops and updates laboratory testing protocols, reference virus panels that are provided to the GISRS network at no cost, and periodic global surveillance publications that enable NICs and partner laboratories to detect reduced susceptibility to antiviral medicines. The latest protocol, developed by the WHO Collaborating Centre at Japan's National Institute of Infectious Diseases, was recently published on the WHO website.
These efforts are supported by a strong global laboratory network. More than 50 NICs currently conduct antiviral susceptibility testing, and 94% of laboratories participating in the 2025 WHO External Quality Assessment Programme (EQAP) returned fully correct results.
The AVWG also continues to monitor newly developed antiviral medicines, assess emerging mutations that could affect their effectiveness, and develop the tools needed to detect them.
Looking ahead
As the working group marks 15 years of service, members agreed to strengthen preparedness for future public health emergencies. Current priorities include developing an emergency response framework for GISRS, establishing mechanisms to rapidly assess and respond to emerging antiviral resistance signals, and increasing awareness of the importance of antiviral susceptibility surveillance.
The group also plans to publish a global analysis of antiviral susceptibility surveillance results from 2023–2026 and launch a series of webinars and additional resources to further strengthen surveillance capacity across GISRS in 2027.
The 16th AVWG meeting is planned for June 2027.