Risk assessment H5 clade 2.3.4.4b viruses

Overall, the risk of infection with avian influenza viruses of the clade 2.3.4.4b which is currently circulating in Europe, is considered to be low for the general public in EU/EEA countries. The risk for occupationally or otherwise exposed groups to avian influenza-infected birds or mammals is assessed as low to moderate.

The likelihood of travel-related importation of human avian influenza cases from countries where the viruses are detected in poultry or wild birds, is considered to be very low.

Reassortment events will likely continue globally, thereby leading to a more complex situation which may be challenging for a general risk assessment.

The risk assessment is based on the following aspects:

• Avian influenza virus transmission to humans remains a rare event.
• Viruses currently circulating in bird populations in Europe are considered to be avian-adapted viruses.
• Despite the large number of human exposure events to clade 2.3.4.4b viruses in Europe over the last three years, no symptomatic infection has been identified and reported.
• Mutations associated with mammalian adaptation have been identified sporadically in a few birds, but emerged more frequently in mammalian hosts after infection. No mutations or reassortment have been identified that would modify the virus to become human-adapted and transmissible between humans.
• No mammal-to-human transmission or cluster with limited human-to-human transmission has been observed recently.
• The majority of avian influenza A(H5N1) viruses currently circulating in Europe are susceptible to all licensed antivirals for use in influenza infections. Only a few viruses have been observed that have mutations associated with resistance to antivirals, such as neuraminidase inhibitors (NAIs).
• There are no indications thus far that the avian influenza A(H5N1) viruses currently circulating in the EU/EEA differ antigenically from proposed candidate vaccine viruses for pandemic preparedness.  

Sporadic symptomatic and severe human infections with A(H5N1) viruses that have been reported globally underline the risk of infection when people are directly exposed to infected sick or dead birds without any kind of protection.

While the risk to humans is considered very low for viruses adapted to avian receptors, the likelihood of zoonotic transmission of avian influenza viruses cannot be excluded when there is exposure to avian influenza viruses present in birds.