Research and analysis

HPR volume 16 issue 7: news (29 July 2022)

Updated 30 December 2022

UK seasonal influenza annual report 2021 to 2022 in summary

The UK Health Security Agency (UKHSA) has published its 2021 to 2022 annual flu reports, summarising the surveillance of influenza and other seasonal respiratory viruses in winter 2021 to 2022, as well as end-of-season influenza vaccine uptake in GP patients, in frontline healthcare workers and in children of school age.

Outputs from multiple surveillance systems are presented covering influenza and other non-COVID-19 respiratory virus activity, along with a summary of emerging respiratory virus activity. Influenza vaccine uptake figures and vaccine effectiveness estimates for the 2021 to 2022 season are also presented.

During the 2021 to 2022 season up to week 14 of 2022, 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 levels observed in previous seasons. Low-level increases in influenza activity were first observed in 2021 through several indicators, before COVID-19 Omicron control measures from late November 2021 suppressed influenza transmission. Influenza subsequently increased in multiple indicators up to week 14 of 2022, representing late-season activity.

Influenza A(H3N2) was the predominant subtype, with low-level influenza 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

Influenza vaccine uptake in England varied by cohort during 2021 to 2022. Uptake in those aged over 65 was the highest ever achieved at 82.3%. Uptake in those aged 6 months to under 65 years clinically at-risk was similar to last season, at 52.9%. For other cohorts, vaccine uptake was slightly below levels observed in 2020 to 2021 at:

• 50.1% in 2 and 3 year olds
• 37.9% in pregnant women
• 61.4% in frontline healthcare workers
• 57.4% in primary school-age children

The influenza vaccination programme was extended in all secondary school-age children to those aged 11 to 16 years, with 43.6% uptake achieved.

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%).

Respiratory syncytial virus activity was relatively low between week 40 of 2021 and week 14 of 2022, after out-of-season increases in the summer of 2021 were observed.

Surveillance of influenza and other respiratory viruses is ongoing, with weekly data published in the UKHSA weekly national influenza and COVID-19 surveillance report.

Transfusion transmitted infections (UK): 2021 annual report in summary

Transfusion transmitted infections (TTIs) remain extremely rare in the UK due to risk reduction strategies including donor selection and rigorous testing of blood donations. All suspected TTIs investigated by the UK blood services are reported to the joint NHS Blood and Transplant (NHSBT) and UKHSA Epidemiology Unit for monitoring and form part of the Serious Hazards of Transfusion (SHOT) haemovigilance scheme.

This news report summarises the findings of the 2021 Annual SHOT Report which has been published on the SHOT website.

During 2021, the UK blood services investigated 115 suspected bacterial cases and 10 suspected viral incidents none of which were confirmed as TTIs.

All of the suspected bacterial cases were concluded to be either a post-transfusion reaction with no evidence of bacteria in the implicated or associated products or in the recipient, or not a TTI, with evidence of bacteria in either the products or the recipient(s) but not both. In all cases where patient blood cultures were positive, the likely source was the patient’s underlying condition. All 4 UK blood services use the BacT/ALERT system for bacterial screening which has contributed to reducing the risk of bacterial TTIs. The last confirmed bacterial TTI – a Staphylococcus aureus – was reported in 2015.

Viral transmissions are extremely rare in the UK, with only 42 documented, involving 35 donors, since 1996. Among these, Hepatitis B virus (HBV) (n=12) and Hepatitis E virus (HEV) (n=12) were the most commonly reported proven viral TTI. For recently acquired HBV, this is partly because the ‘window period’ – during which an infectious donation from a recently infected donor cannot be detected by the screening tests – is longer than for Hepatitis C virus (HCV) or human immunodeficiency virus (HIV), despite nucleic acid testing (NAT) screening of blood donations. For HEV, all except 2 transmissions were reported before the HEV RNA screening was introduced in April 2017 in the UK.

Repeat-donor lookbacks

Included in this year’s SHOT report are the results of lookback investigations into possible TTIs, carried out during the last 3 years. Lookback investigations are considered when the UK blood services identify markers of infection in a donation from a repeat donor. This may be due to seroconversion or the introduction of a new test, or for occult hepatitis B infection when DNA is detected but donation was previously screen negative. This is different to the other investigations reported here that are initiated due to a potential TTI in a recipient.

For lookbacks, where possible, archive samples from previous donations are retrospectively retested and, regardless of archive availability, associated components are traced. The blood services – working with the clinical team – look after the recipient to ensure that they are fully informed and are given advice regarding follow-up and testing. Between 2019 and 2021, NHSBT identified 5 HEV, 12 syphilis and 4 occult HBV donors with previous donations identified as positive in retrospective testing. From these, a total 46 of 55 components were transfused, and all 46 recipients identified. Of those recipients who were alive, 22 of 30 were tested and 2 were positive for markers of hepatitis B infection and 1 HEV. These infections in recipients were concluded as a probable HBV and a confirmed HEV transmission and were reported in SHOT 2020 and 2019 reports respectively. The remaining HBV infection was classified as a possible TTI as the recipient had markers of past HBV but another source was as likely. One HEV lookback investigation was undertaken by Scottish National Blood Transfusion Service in 2021 but there was no evidence of transmission.

Further information about these cases is available in the TTI chapter of the annual SHOT report.

Key messages from the new SHOT report are as follows.

1. Any suspicion of a transfusion-transmitted infection (TTI) should be reported to the appropriate UK blood service as soon as possible for it to be fully investigated.
2. The UK blood services store a sample from every blood donation for at least 3 years – testing can be done on these samples during this time if a TTI is suspected.
3. All lookback investigations should be reported by the UK blood services to the infectious disease expert sitting on the SHOT working expert group.
4. It is important that all healthcare professionals consenting patients for blood transfusion have up-to-date knowledge of blood donation screening and the small potential for TTI.

Further information about UK TTI surveillance is available from the NHSBT and UKHSA Epidemiology Unit: epidemiology@nhsbt.nhs.uk

Infection reports

Laboratory confirmed non-COVID-19 respiratory infections (England and Wales) in 2022: to week 28.