Operational considerations for influenza surveillance in the WHO European Region during COVID-19: interim guidance

Key messages

For sentinel primary care influenza surveillance:

• It is important to maintain existing influenza-like illness (ILI) and acute respiratory infection (ARI)case definitions, where possible.
• When the number of cases presenting to sentinel surveillance sites is low, all patients meeting the case definition for ILI or ARI should be sampled.
• Sampled patients meeting the ILI or ARI case definition should ideally be tested concurrently for influenza and SARS-CoV-2 viruses.
• Epidemiological data on ILI should continue to be collected.
• Perform subtyping/lineage determination for all influenza-positive specimens.
• Where sentinel primary care surveillance for influenza has been disrupted because of COVID-19 testing strategies, explore alternative approaches such as patient self-sampling and the utility of telephone consultation syndromic data.

For non-sentinel surveillance:

• Non-sentinel specimens from primary and secondary care should be prioritized for COVID-19 testing; in addition, influenza testing should be performed in parallel for people at risk of developing severe disease (the elderly and those with underlying diseases).
• A random sample of all patients in these settings could be considered for influenza testing, based on clinical judgement and the level of influenza circulation, including further genetic and/or antigenic characterisation and antiviral resistance testing at national influenza centres or reference laboratories.

For hospital influenza surveillance:

• Important to maintain existing SARI case definition, where possible
• Test and report all SARI cases for influenza and SARS-CoV-2 simultaneously, where possible when influenza is known to be circulating

Laboratory considerations:

• Sequence a representative subset of influenza and SARS-CoV-2 viruses (date, geographical region, age, severity).
• Share a representative subset of influenza-positive specimens with national influenza centres or reference laboratories.
• At least 10% of the influenza viruses, or all when low circulation observed, should be characterised genetically and/or antigenically.
• At least 10% of the influenza viruses, or all when low circulation observed, should be tested (phenotypically and/or genotypically) for antiviral resistance