Infections of SARS-CoV-2, or COVID-19, do not always occur on their own. A COVID-19 infection can occur at the same time as an infection of the flu (influenza virus) or common cold (adenoviruses).
It is thought that co-infections of SARS-CoV-2, influenza viruses, and adenoviruses significantly increase the odds of death compared to an infection with a single virus. Co-infections have also been shown to increase the likelihood of needing mechanical ventilation during a SARS-CoV-2 hospitalization. Due to the increased risk of severe disease, co-infection of COVID-19 and influenza should be avoided whenever possible.
A new study published in Virology examines the frequency of SARS-CoV-2 and influenza co-infection in Missouri during the 2021-2022 influenza season. The flu season typically lasts from October to May in the United States, during the year's colder months.
The researchers found that during the 2021-2022 flu season, co-infections of influenza and COVID-19 rose as high as 48% during the month of October. At that point in time, the prevailing COVID-19 variant was the Delta variant.
By the month of January, the rate of co-infection had dropped to around 7% when the Omicron variant prevailed. The researchers found that individuals were less likely to become co-infected with the flu and COVID-19 if they had received an influenza vaccine during the current or previous flu season. They also found that those infected with the Omicron variant were less likely to be co-infection with the flu and COVID-19.
Henry Wan, Ph.D., study co-author, says that “our study highlights the importance of influenza vaccinations, as they appear to not only offer some protection against influenza infections but, importantly, against COVID-19 and flu co-infections.”
The researchers involved in the study also recommend that clinicians test patients experiencing respiratory symptoms for influenza at the same time that they test for COVID-19.