The co-circulation of SARS-CoV-2, the virus causing COVID-19, and seasonal influenza viruses has raised public concern about simultaneous infection. Co-infection, sometimes informally called “Flurona,” refers to an individual being infected with two different pathogens at the same time. Testing positive for both SARS-CoV-2 and Influenza simultaneously is possible. The potential for these two widespread viruses to infect the same host during seasonal overlap presents unique challenges for public health and clinical management.
Is Testing Positive for Both Possible?
The possibility of contracting both SARS-CoV-2 and Influenza is supported by the distinct biological mechanisms these viruses use to infect the respiratory tract. While they both target the airways, SARS-CoV-2 primarily uses the Angiotensin-converting enzyme 2 (ACE2) receptor to enter human cells, whereas the influenza virus utilizes sialic acid receptors. Because the viruses use different cellular entry points, they can coexist within the same host, leading to a co-infection.
The co-infection rate has varied significantly across different studies and geographic regions. As COVID-19 becomes a more endemic, seasonally circulating virus, the likelihood of co-infection increases whenever influenza activity rises, typically during the fall and winter months. The return to pre-pandemic social patterns and the co-circulation of both pathogens have made co-infection a recurring concern during flu seasons.
What Are the Symptoms and Risks?
The symptoms of co-infection with COVID-19 and Influenza largely overlap, making it impossible to differentiate between the two viruses based on self-diagnosis alone. Both can cause fever, cough, fatigue, sore throat, and headaches. This clinical similarity underscores why laboratory testing is necessary to determine which virus, or both, is responsible for the illness.
Clinical evidence suggests that co-infection often leads to more severe health outcomes compared to infection with only one virus. Patients diagnosed with both SARS-CoV-2 and influenza have been shown to have an increased risk of mortality, with some studies indicating the risk of death is more than double that of those with COVID-19 alone. This also translates to higher rates of hospitalization, increased need for intensive care unit (ICU) admission, and a greater requirement for mechanical ventilation.
Vulnerable populations, including the elderly, individuals with underlying chronic conditions, and those who are immunocompromised, face the highest risk of severe illness from co-infection. The dual viral attack can lead to prolonged inflammatory responses, severe pneumonia, and greater lung damage. A co-infection may also impair the body’s immune response, potentially resulting in reduced neutralizing antibody titers against each virus.
How Are Both Viruses Diagnosed?
Accurately diagnosing co-infection is a necessary step for proper clinical management and timely treatment, particularly since both influenza and COVID-19 can benefit from early antiviral therapy. Because the symptoms are nearly identical, healthcare providers rely on specific laboratory methods to identify the causative agents. The primary tool for this purpose is multiplex testing, a diagnostic assay that can detect multiple respiratory viral pathogens from a single nasal or throat swab sample.
Multiplex tests are typically molecular assays, such as real-time Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR), which simultaneously screen for SARS-CoV-2, Influenza A, and Influenza B. This method is highly sensitive and allows for rapid differentiation between the viruses, which is important when both viruses are widely circulating. Some multiplex tests are also available as rapid antigen tests (RATs), providing a quicker result, though PCR remains the preferred method for its higher sensitivity.
Protecting Yourself Against Co-Infection
The most effective strategy for preventing co-infection is maximizing protection against both respiratory pathogens through vaccination. Getting the annual influenza vaccine and staying up-to-date with the latest COVID-19 booster shot are the principal preventative measures. These vaccines target different viruses and can be safely administered during the same visit without compromising their effectiveness. Vaccination not only reduces the risk of contracting each virus but is also proven to lessen the likelihood of severe illness, hospitalization, and death if an infection occurs.
Beyond vaccination, general public health practices continue to play an important role in reducing transmission risk. Practicing frequent and thorough handwashing helps eliminate viral particles acquired from surfaces. Wearing a high-quality, well-fitted mask in crowded indoor settings or during periods of high community transmission provides a physical barrier against respiratory droplets. Additionally, individuals who experience any respiratory symptoms should stay home to prevent spreading the infection to others, especially those at high risk for severe outcomes.