An influenza infection could inhibit a simultaneous Sars-Cov-2 infection. This is the result of researchers from the USA in a study in the “Journal of Virology”.
Using cultured cells and animal experiments with hamsters, the scientists led by Kohei Oishi from New York University found that the influenza A virus impairs the multiplication of the coronavirus in the lungs – even more than a week after the influenza infection.
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The research is important because, with Sars-Cov-2 and Influenza A, two RNA viruses are currently circulating in the human population that have a high pandemic potential, the researchers write. Since both viruses infect the respiratory tract and can cause severe courses and even death, it is “imperative” to understand the consequences of co-infection.
The researchers infected hamsters with both viruses at the same time and then examined the animals regularly. They also conducted experiments in which they first infected the animals with one of the two viruses and three days later with the other virus.
In some of the co-infected hamsters, the amounts of Sars-Cov-2 in the lung tissue were lower than in animals that were only infected with the coronavirus. If, on the other hand, the hamsters were first infected with Sars-Cov-2, this infection apparently had no effect on the replication of the influenza viruses introduced later.
The reduced multiplication of the corona virus after infection with the flu pathogen came together with higher interferon levels. These messenger substances stimulate the production of antiviral proteins in cells. Interferons are part of the innate immune system. Overall, the host’s response to both viruses is comparable to that of an infection with only Sars-Cov-2.
“The phenomenon described, that a virus apparently tries to prevent a second virus from entering the cell, has been known for many decades,” said Ortwin Adams, virologist at the University Hospital Düsseldorf the Science Media Center Germany (SMC).
The term “viral interference” used for this is also the namesake for the interferons that are effective here. “The influenza virus is known to be a virus that produces a strong interferon response in the infected cell,” says Adams.
According to the researchers, the co-infection study could serve as an example of how an immune response to something unrelated could offer protection against Sars-Cov-2. The data suggested that co-infection with Sars-Cov-2 and influenza is unlikely to lead to more severe illness. Previous studies, such as those recently published in the specialist journal “The Lancet”, have shown increased mortality rates in the case of co-infections with both pathogens.
“The flu puts the hamster’s organism into an antiviral status, in which interferon-stimulated genes are upregulated after infection,” explained Stephan Becker, head of the Institute of Virology at the Philipps University of Marburg, to the SMC.
This is the body’s natural defense reaction to foreign organisms or substances. “According to the results of this study, this native immune response apparently inhibits Sars-Cov-2 more than is the case with influenza,” says Becker.
However, the hamster model does not allow any general conclusions. “I would not rely on hamster data to assume that co-infections are harmless,” says Becker. The animal model is “closer to humans” than cell cultures, says Adams, but the immune system is not the same as that in humans.
“In addition, the animals had not had any contact with influenza or Sars-Cov-2 until the experiment,” says the virologist. However, adults have decades of experience with influenza viruses and Covid-19 vaccinated and recovered also with Sars-Cov-2.
For basic statements, people would have to be examined – before, during and after co-infections. In addition, the vaccination status of the study participants and the variants of the viruses would have to be taken into account. Two older virus variants were used in the study. “Newer virus variants could have a different, possibly more pathogenic effect if you are infected with both pathogens,” says Becker.
He and Adams recommend building up a broad vaccination protection against Sars-Cov-2 and against influenza for the fall and winter. “In this way, we are quite certain to minimize the risk of possible co-infections, especially for older people.”