Surveillance of influenza and other seasonal respiratory viruses in winter 2021 to 2022 - GOV.UK - ISS-G20 Laboratorium Repository

This report describes surveillance findings for seasonal influenza, other seasonal respiratory viruses and the monitoring of human cases of avian influenza and Middle East Respiratory Syndrome coronavirus (MERS-CoV).

In the 2021 to 2022 season (from week 40 of 2021 to the week 14 of 2022 reporting cut-off), low levels of influenza activity were seen across the UK, with most indicators remaining below baseline for the majority of the season. Although activity was generally higher than levels observed during the 2020 to 2021 season, it remained much lower than those in previous seasons.

Through several indicators, low level increases in activity were observed first in 2021 before coronavirus (COVID-19) Omicron control measures from late November 2021 suppressed influenza transmission. Influenza subsequently increased in multiple indicators up to week 14 of 2022 (declining thereafter, data not shown), representing late-season activity.

Influenza A(H3N2) was the predominant subtype, with low-level influenza type B Victoria lineage in 2021 and influenza A(H1N1)pdm09 detections becoming more prominent in 2022 though still a small proportion of subtyped viruses. Of the genetically characterised influenza A(H3N2) detections, the majority were in the subclade 3C.2a1b.2a.2.

Due to the COVID-19 pandemic, data reported from the various influenza surveillance systems should be interpreted with caution. Increases seen in some indicators may not accurately reflect influenza activity but rather COVID-19 activity, and that of other respiratory pathogens.

Interpretation of influenza surveillance data should take into account the effect of public health messaging and other non-pharmaceutical interventions, as well as potential changes in health seeking behaviours due to COVID-19 activity.

In primary care, GP influenza-like illness (ILI) consultation rates across the UK remained below baseline intensity levels for the duration of the 2021 to 2022 season. Rates were generally higher than those observed in the 2020 to 2021 season, however remained much lower than rates observed in seasons prior.

In secondary care, both hospital and critical care (ICU or HDU) influenza admissions remained below the baseline threshold levels for the majority of the season, with hospital admissions rising slightly above the baseline in week 12 and week 14 of 2022. While rates were higher than those observed in 2020 to 2021, admissions were lower than those seen in previous seasons.

Provisional end-of-season vaccine effectiveness (VE) was 26% (95% confidence interval (CI) 5% to 43%) against all laboratory-confirmed influenza illness in adults aged 50 years and over. For children aged 1 to 17 years, VE was 73% (95% CI 53% to 84%).

Adults aged 50 to 64 years old were again offered the flu vaccine in 2021 to 2022, after the supply-dependent extension of the programme to this cohort in 2020 to 2021. The childhood programme was also extended in secondary school children across the UK up to the school leaving age (the school year in which children turn 16 years of age).

Vaccine uptake in England varied by cohort for the 2021 to 2022 season. Vaccine uptake in those aged 65 years and over was at 82.3% compared to 80.9% in 2020 to 2021. This is the highest uptake ever achieved in this cohort, and is likely to reflect the continued awareness of the protection from vaccination since the COVID-19 pandemic.

For other cohorts, vaccine uptake was slightly below levels observed in 2020 to 2021, with uptake in 2 and 3 year olds at 50.1% compared to 56.7% in 2020 to 2021. Vaccine uptake in those aged 6 months to under 65 years clinically at-risk was similar to last season, at 52.9% compared to 53.0% in 2020 to 2021.

Vaccine uptake in pregnant women in England in the 2021 to 2022 season was 37.9%, compared to 43.6% in 2020 to 2021.

The 2021 to 2022 season saw 61.4% of all frontline HCWs with direct patient care (from all organisations submitting data) receiving the influenza vaccine in England, down from 76.8% in the 2020 to 2021 season. This is lower than the uptake observed in this cohort in the previous 5 seasons.

The influenza vaccination programme in the UK for school-aged children was extended in secondary school aged children in 2021 to 2022. Vaccine uptake in all primary school age children in England (age 4 to 11 years old) was 57.4% compared to 62.5% in 2020 to 2021. Vaccine uptake in all secondary school age children in England (age 11 to 16 years old) was 43.6%.

Activity from other circulating seasonal respiratory viruses, including respiratory syncytial virus (RSV), was generally higher than levels observed in 2020 to 2021 but lower than levels in pre-pandemic seasons. RSV activity was relatively low between week 40, 2021 and week 14, 2022 after out-of-season increases in summer 2021.

Novel and emerging respiratory viruses including MERS-CoV and avian-origin influenza viruses, have continued to result in human cases in affected countries. There have been multiple detections of avian influenza in avian species in the UK in 2021 to 2022 as reported by the Department for Environment, Food and Rural Affairs (DEFRA).

The UK reported a first human case of influenza A(H5N1) in January 2022 in a person directly exposed to infected birds, with no evidence of onward transmission.

Surveillance and public health measures are recommended in the UK for persons potentially exposed to infected birds and for severe respiratory disease among travellers returning from affected countries.

Entire content available on: https://www.gov.uk/government/statistics/annual-flu-reports/surveillance-of-influenza-and-other-seasonal-respiratory-viruses-in-winter-2021-to-2022