On Jul. 2, 2020, the U.S. Centers for Disease Control and Prevention (CDC) announced a publication in the journal Proceedings of the National Academy of Science that described a group of H1N1 swine influenza viruses that have ‘the essential hallmarks of being highly adapted to infect humans’ and which are therefore of potential pandemic concern.

This group of viruses, referred to as “G4” Eurasian (EA) avian-like H1N1 viruses, has been spreading in pigs in China since 2016 and has become the predominant genotype found in Chinese pigs. According to the report, these viruses have the right characteristics for causing infections in people, including the ability to grow well in human lung cells and to spread by respiratory droplets and direct contact in an animal model.

While only three human infections with G4 viruses have previously been reported, this study found that about 10% of swine workers from whom blood samples were taken in China had evidence of prior infection with G4 viruses, suggesting that human infection is more common than previously thought.