Rapid Risk Assessment: Risk to UK consumers from Highly Pathogenic Avian Influenza (HPAI) H5N1 B3.13 in US dairy products

The probability that UK consumers will receive potentially infectious exposures to influenza of
avian origin via imported US dairy products is assessed to be Very Low, due to the low amount
of dairy products consumed in the UK that are imported from the US, the high proportion of those
imports undergoing processing which is considered highly likely to inactivate any infectious virus
present, and the assumed low oral infectivity of influenza virus for humans. “Very Low” is defined
as “Very rare but cannot be excluded”. The probability is not Negligible because although highly
likely, it is not certain that dried milk powder imported from the US has undergone sufficient
processing to eliminate any infectious virus present. Confirmation of this would reduce the
probability to Negligible.
The uncertainty in this estimate is Medium, largely because of uncertainty around the proportion
of imported powdered milk which is freeze-dried, and the effect of those freeze-drying methods on
virus infectivity (and given that most milk imported to the UK is for powdered milk production).
“Medium” is defined as “There are some but no complete data available; evidence is provided in
small number of references; authors report conclusions that vary from one another”. Because the
uncertainty is “Medium” and this is a rapidly evolving situation, any new evidence that may require
this rapid risk assessment to be updated will be actively monitored for.
In the event of infection, the severity of detriment is assessed as Low. The single confirmed case
of human infection so far reported eye redness (consistent with conjunctivitis) as their only
symptom (CDC, 2024), but is not believed to have been exposed via the consumption of
contaminated products. The individual was treated with antivirals as a precaution, so it is unclear
whether this would have resolved or progressed. “Low” is defined as “Mild illness: not usually lifethreatening, usually no sequelae, normally of short duration, symptoms are self-limiting (e.g.
transient diarrhoea)”.
The uncertainty in this severity is High which reflects the recent emergence of this strain, the
limited clinical data on infection with this strain so far, and the fact that reporting disincentives
make it difficult to be certain that other human infections have not occurred. “High” uncertainty is
defined as “There are scarce or no data; evidence is not provided in references but rather in
unpublished reports or based on observations, or personal communication; authors report
conclusions that vary considerably between them”. However, in the event that someone is
severely affected by an influenza-like illness in the US they would normally report to medical
professionals and be hospitalised and tested. There is therefore some level of confidence that this
strain is not resulting in large numbers of severe infections.
This document specifically assesses the risk from the strain involved in the current spill over
outbreak in US dairy cattle. Strains of influenza vary widely in their clinical presentation in infected
humans. However, the majority of human cases of influenza of avian origin have been associated
with Asian genotypes or clades. For influenza of avian origin as a whole (in this case, ingested via
poultry products), the severity is considered to be High with Medium uncertainty (Kintz et al.,
2023).
Limitations of this assessment
This assessment only considers the risk associated with current outbreak of B3.13 in the US. It
does not consider:
1. Speculation on the likelihood, timescale, and potential future routes of introduction into the
UK, including via wild bird migration routes;
2. Assessment of the ability of existing surveillance processes such as syndromic
surveillance, pre- and post-mortem inspections at slaughter, etc, to detect the presence of
this strain in UK cattle;
3. Occupational risk to those working with cattle or in food production;
4. Risks to the health of UK animals (e.g. livestock and companion animals);
5. Consumer risks from beef or any products of animal origin other than dairy;
Key uncertainties
There are two key areas in the risk assessment where additional information would reduce
uncertainty levels assigned:
There is significant uncertainty around the amount of colostrum currently imported into the UK,
its uses, and the processing it undergoes.
The vast majority of dairy imported into the UK is dried milk powder, and it is not clear whether
this production method always involved pasteurisation or whether, if it does not, the drying
process used will be effective at inactivating any infectious virus present. In particular, one
method of producing powdered milk (freeze-drying) avoids the use of high temperatures. It is
considered likely that milk is pasteurised before this process, the process itself would inactivate
infectious virus present, or both, but verification of this assumption could reduce the estimated
risk for UK consumers.