Pig farmers in China are being infected by a new, virulent strain of influenza A that they contracted from their swine, said a speaker at an Infectious Diseases Society of America (IDSA) news conference last week.
About 15% of Chinese pig farmers have tested positive for antibodies to the new disease, said Leonard Mermel, DO, professor of medicine at the Warren Alpert Medical School of Brown University and medical director of the Department of Epidemiology and Infection Control at Rhode Island Hospital in Providence.
“Unfortunately, this influenza strain has all the attributes to cause a pandemic,” he said. “It’s easily taken up by human cells. It can be spread in an animal model — ferret to ferret through respiratory secretions. The ferrets that get infected have worse outcomes than seasonal influenza.”
This unique strain, he added, “is more virulent and more infectious and has worse outcomes than human influenza A.”
According to a study in the Proceedings of the National Academies of Science, pigs in China are increasingly becoming infected with an influenza virus dubbed G4. The virus is said to be a hybrid of strains found in European and Asian birds: the H1N1 strain that caused the 2009 pandemic, and a North American H1N1 strain that has genes from avian, human, and pig influenza viruses. The PNAS study states that 10.4% of “swine workers” had tested positive for G4.
In light of the information about the new swine flu, Mermel said, work on a universal influenza vaccine should be accelerated.
“A worst-case scenario would be if this started spreading in the fall, at the time when we’re concerned about COVID-19,” he said. “We’ve got to get a universal flu vaccine before this virus, which is locked and loaded and ready to go, spreads from Chinese pig farmers to other parts of Eurasia and other parts of the world.”
Such a vaccine, which would prevent infection by most influenza A and some influenza B viruses, is currently in stage 1 testing at the National Institutes of Health, Jeanne Marrazzo, MD, a professor of medicine and director of the Division of Infectious Diseases at the University of Alabama at Birmingham, said during the IDSA conference.
Nor is this the only non-COVID pandemic threat, Mermel added. He mentioned an influenza virus called H7N9, which has spread in some parts of China and “has a very high associated morbidity and mortality.”
One new reason to get flu shots, Marrazzo said, is that “you need every protection you can get against COVID-19. You also don’t want to be exposed to COVID-19 when you’re sick from another virus. Immunosuppression will make it harder to fight COVID.”
One reporter asked how likely it would be to get infected with COVID-19 and influenza at the same time and what the result might be. Mermel replied, “At Rhode Island Hospital, we had a low number of coinfections by influenza and COVID-19 in the last flu season.”
The medical literature indicates that such coinfections can occur, but it is unclear as to whether they lead to worse outcomes than occur with COVID-19 alone, he added.
The flu season in the Southern Hemisphere — particularly in South Africa and Australia — was milder than normal this year, Mermel noted. One reason might be that some countries adopted strict mitigation polices for COVID-19, which also limited the spread of influenza, he said. However, he noted, the flu season in the United States might be quite severe, especially if some Americans continue to resist mitigation measures, such as mask-wearing and social distancing.
A big part of the difference between the United States and other nations in this respect is related to messaging from national leaders, Marrazzo said.
“We haven’t had a consistent national message for almost any aspect of pandemic control, whether it relates to how severe the illness is, whether masks are important, and when we’re going to get a vaccine,” she noted.
“If we could have anything [positive] for this winter season, it would be to have a reliable, trusted, consistent national message from trusted, scientifically informed leaders to get us through this. That’s what we need.”