#19,281
Despite being of the same subclade (2.3.4.4b) the HPAI H5N1 viruses circulating in the UK (and Europe) during the 2023-2025 were (and remain) genetically distinct from those circulating in North America.
This matters because even minor differences in HPAI strains (subtypes, genotypes, Amino Acid changes) can alter the transmissibility, host range, and virulence of the virus.While cattle-associated genotype B3.13 and a newly emerged genotype D1.1 both emerged in North America in 2024, the UK and Europe were dealing with a combination of EA-2024-DI and DI.2/D1.2 genotypes.
With that in mind, today we have a research report published yesterday in Eurosurveillance that finds relatively limited evidence of infection of workers exposed to infected poultry in the UK.
The time period covered (Apr 2023 - Mar 2025) saw 60 outbreaks in England (see chart below), but recruitment was done only at 34 premises (57%), and was confined to England (excluding Scotland, Wales & Northern Ireland).
Out of 862 potentially exposed individuals from these 34 premises, roughly half (n=428) were enrolled in the study. Of those, 3 were determined to have been infected, while three others had positive tests that were most likely due to contamination and not infection.
This provides a substantial - albeit incomplete - occupational sample, but it likely only captures a fraction of those exposed in the UK during this time.
And in the 16 months since this survey ended, the UK has reported a surge of roughly 115 additional HPAI outbreaks (note: 15 cases were reported over the summer of 2025).
While this study provides a useful snapshot of the risks of the H5N1 viruses circulating in England during the 2023-2025 study period - given HPAI's continued evolution - it isn't necessarily predictive of the risks going forward.
It does, however, illustrate the value of PPE use and other biosecurity measures in contaminated environments.
Due to its length I've just posted the link and some extended excerpts from the study. Follow the link to read it in its entirety.
A cohort study of persons exposed to highly pathogenic avian influenza A(H5N1) at premises with infected animals, England, 2023 to 2025
Florence Halford1 , Paula B Blomquist1 , Neil Bray1 , Chloe Byers1 , Carmellie Inzoungou-Massanga1 , Carys Rees1 , Maria Waghorn1 , Motolani Awokoya1 , Rachel Lunt1 , Neil Cunningham1 , Michelle Chapman1 , Philippa Jones1 , Nicholas Machin1 , Georgios Chalikias1 , Alan Lord1 , Rachel Benee2 , Sophia Makki1 , Beatrix Kele1 , Andre Charlett1 , Katja Hoschler1 , Anika Singanayagam1 , Maria Zambon1 , Oluwakemi Olufon1 , Obaghe Edeghere1 , Meera Chand1 , Susan Hopkins1 , Deepti Kumar1 , Richard Puleston1
Key public health message
What did you want to address in this study and why?
Following an increase in the number of avian influenza outbreaks in England, we wanted to understand the risk of human infection among people who work closely with birds on farms where outbreaks had occurred. We were interested in whether any individuals with positive tests had any symptoms, and if any steps that were taken to reduce their exposure had an effect on their illness (such as vaccination or use of protective equipment).
What have we learnt from this study?
Less than 1% of participants in this study had an avian influenza infection after working closely with infected animals. None of the participants who had a positive test were vaccinated against seasonal influenza, none had severe symptoms, but the majority reported wearing protective equipment. Although there were some practical challenges, we found recruitment to be more achievable when undertaken in person at the outbreak sites.
What are the implications of your findings for public health?
Being able to better understand the risk of avian influenza infection among farm workers on sites with outbreaks is important for forming public health recommendations and better preparing for future outbreaks. Based on our findings, we recommend continuing proper use of protective equipment and resuming testing of workers at outbreak sites if the risk of human infection increases, to strengthen public health response to future outbreaks.
Discussion
This 2-year surveillance study of avian influenza A(H5N1) among persons exposed at IPs in England identified three cases meeting the criteria for infection (two confirmed, one unclear) and three cases with uncertain significance, deemed likely to have transient mucosal contamination. The low < 1% PCR positivity rate and mild symptoms in cases suggest that there is a low risk of bird-to-human transmission of the 2.3.4.4b clade and of severe disease in humans in the UK, even when exposed by touch, where PPE compliance is robust among most individuals. Comparable studies in the US and elsewhere have reported similarly low rates of human infection, but with varying severity [16,17].
The direct nature of exposure among cases in this study aligns with that of a confirmed human case of influenza A(H5N1) in the UK in January 2022 [18], reinforcing the importance of maintaining distance from infected birds and the critical use of correct PPE, which should be communicated through public health messaging [19]. Four of the six cases in this study reported wearing full PPE when exposed; therefore, it is unclear where the potential exposure occurred for these individuals. This suggests difficulty in ensuring proper PPE donning/doffing and compliance in these environments. The possibility of PPE breaches/not recognising when breaches have occurred or inaccuracies due to recall bias cannot be ruled out, as this information was self-reported via questionnaire. Our findings are consistent with cases in the US, where positivity among exposed persons was low, although occasional transmission events were observed among those with close contact and suboptimal PPE use [16].
Our study had some limitations. The study was stopped before reaching the 1,000 participant target sample size because of resource constraints. Although recruitment uptake was significantly higher when undertaken in person, this was not always feasible because of occasional unavailability of the study team at short notice, limited space on site to undertake safe recruitment as determined by the APHA, or unsuitable conditions such as extreme weather. This highlights a need for substantial resource allocation in future surveillance to increase the recruitment of eligible individuals, and thus the precision of findings. Recruitment on site also proved challenging, as eligible persons raised concerns regarding the security of their data, time requirements, and isolation should they test positive. The latter issue was more common among contractors, where sick pay was not offered and daily government compensation was insufficient to cover loss of earnings, suggestive of unequal participation due to financial insecurity. Language barriers further hindered recruitment among contractors, although translated documents were prepared ahead of time, highlighting that future surveillance programmes need to include more inclusive communication strategies.
Demographic details were not gathered for all eligible persons; thus, we were unable to calculate recruitment uptake by occupation or IMD, which limits the generalisability of our results. However, of those recruited to the study, socioeconomic differences were apparent between the two main occupational groups: the majority of the contractors resided in the lowest IMD quintile, while the majority of APHA staff resided in the three least deprived quintiles. Although all recruited participants were within the biosecurity area at some point during their exposure period, the contractors had the highest proportion exposed by touch (88.8%) and frequently spent long periods of time in sheds containing infected birds, possibly putting them at a higher risk of exposure than others. With this increased risk in mind, extra care should be dedicated to ensuring that risk and control measures (such as PPE policies and symptom awareness) are effectively communicated to all and that all workers comply with them; simple language versions as well as translated materials should be available.
(SNIP)
Conclusions
Our findings suggest that the influenza A(H5N1) clade 2.3.4.4b viruses circulating in the UK during the period 2023 to 2025 pose a low risk of zoonotic infection in exposed individuals, under present conditions.
However, the detection of mucosal contamination among people self-reporting full PPE usage highlights the need for continued vigilance, and potential challenges with fomites. Surveillance within a One Health framework remains essential for detecting emerging variants with pandemic potential and reducing inequalities in surveillance accessibility through innovative and targeted approaches is imperative to ensure populations are not overlooked.
While there are limitations surrounding chemoprophylaxis, PPE use as per guidance can be an effective barrier to transmission; however, care must be taken to ensure compliance. The combination of these preventative measures, continued biosecurity vigilance, and resumed enhanced surveillance following identification of an increased risk of animal-to-human transmission, are required for mitigating the risks posed by influenza A(H5N1) in poultry outbreak settings.