Reduction of virus isolation effectiveness from throat swab double positive to H1N1pdm09 and H3N2 influenza A virus strain with SARS-CoV-2 virus in cell cultures

Background: Influenza virus isolation in cell cultures can be a foremost activity in the surveillance of the epidemiological characteristics involved in the vaccination strategies. Methods and results: Here, the virus isolation effectiveness from double positive throat swab to influenza A virus (H1N1pdm09 or H3N2) and SARS-CoV-2 compared to those obtained from single positive throat swab samples was investigated by serial passages of throat swabs samples in cell cultures. Viral replication and IFN-α, IL-1α, and IL-6 cytokine expression at three passages were measured by RT-PCR amplification. Virus isolation using a throat swab samples resulted double positive to influenza A virus (H1N1pdm09 or H3N2) and SARS-CoV-2 showed a different effectiveness compared to a throat samples single positive to each of these viruses. The virus isolation efficacy was independent from an active replication of the two viruses in the inoculum and showed a virus strain-specific reduction in cytokines profile compared to a single infection. Conclusion: Collectively the results point out to take into account the presence of co-circulating respiratory viruses in human samples for virus isolation effectiveness.