Could avian influenza A(H5N1) cause a new pandemic?

Avian influenza is one of the most devastating animal diseases. It has a huge economic and sanitary impact and, in some instances, it represents a great risk for public health. Since late 2020 we are experiencing the most severe avian influenza epidemic in history, caused by the highly pathogenic subtype H5N1, belonging to clade 2.3.4.4b. This strain is causing important modifications in the epidemiology of the virus that have never been observed before: (1) a widely extended geographical distribution that confers the character of a panzootic, (2) occurrence of outbreaks throughout the year, unlike the previous seasonal patterns in autumn and winter, (3) high mortality rates not only in poultry, but also in wild birds and (4) more frequent spillovers from birds to mammals. In order to prevent the transmission of the virus from wild birds to poultry, it is important to improve the biosecurity of poultry farms, establish active and passive virological surveillance programs, assess vaccination strategies for domestic birds and develop real-time alert systems that are able to predict periods and areas at high risk for disease introduction. Although avian influenza viruses have limited capacity to jump to humans, this risk should not be underestimated, especially in the current situation with extremely high viral circulation in animals. In Spain, the National Center for Microbiology closely monitors all human cases of influenza A that are negative for the H1 and H3 seasonal subtypes, especially in patients who have contact with animals. For the prevention and control of this zoonosis it is essential to establish an effective and stable collaboration between professionals of the animal health, public health and environmental sectors.