What happens if you catch more than one virus during the flu season?
While secondary infections are commonly observed in influenza, SARS-CoV-2, RSV, and other respiratory viruses, questions remain regarding whether simultaneous infections with these viruses affect disease severity and duration. Following two years of interrupted flu seasons due to the COVID pandemic, we are seeing unusual patterns of influenza, RSV, and other infectious disease outbreaks around the world. Given the simultaneous circulation of multiple respiratory viruses, coinfection with common respiratory viruses such as influenza, SARS-CoV-2 and RSV remain a major concern for public health. Especially with the increasing number of SARS-CoV-2 and influenza coinfections reported from around the world, it is a major issue that SARS-CoV-2 coinfection with other viruses may increase disease severity and mortality rate. So, what happens if you catch more than one virus during the flu season? Read along to learn more about coinfections, superinfections, and their possible pathogenic and immunological consequences for public health.
What causes co-infections with influenza, SARS-CoV-2, RSV, and other respiratory viruses?
A coinfection occurs when a patient is infected with more than one pathogen at the same time. One of the most common and consequential examples of coinfection involves tuberculosis and HIV. Despite their similar clinical presentations, common respiratory viruses cause completely independent infections, which allows for co-infections among them. Accordingly, while the prevalence estimations vary significantly, viral and bacterial coinfections are commonly observed with respiratory viral diseases such as COVID-19, influenza, and RSV. For instance, testing 1217 specimens for COVID-19 and other respiratory pathogens, Kim et al. (2020) have found that around 20.7% of the 116 specimens positive for SARS-CoV-2 have also tested positive for one or more additional pathogens. Likewise, testing 257 laboratory-confirmed COVID-19 patients for 39 respiratory pathogens, Zhu et al. (2020) found that 94.2 % of the patients were co-infected with one or more pathogens, and the prevalence of coinfection has increased in parallel with disease severity.
What are superinfections?
According to the CDC, a superinfection is an “infection following a previous infection, especially when caused by microorganisms that are resistant or have become resistant to the antibiotics used earlier”. Unlike coinfections which occur simultaneously, superinfections follow the initial infection. Superinfections are commonly observed with viral respiratory diseases. In fact, according to Klein et al. (2016), coinfections and superinfections may complicate up to 65% of all laboratory-confirmed influenza-infected patients. Superinfections have also been reported as a complication among patients infected with SARS-CoV-2. For instance, according to a 2020 Italian National Institute of Health report, superinfections accounted for 8.5% of the 3,200 COVID-19-related deaths.
How do coinfections and superinfections impact disease severity?
The exact implications of coinfections and superinfections for disease severity and duration remain unclear. On the one hand, various studies have found no clinical differences among patients with single and multiple respiratory infections, including disease severity, symptoms, and duration. Especially for coinfections with types of influenza and RSV, some studies had further suggested instances of pathogen co-suppression, when infection with one pathogen reduced the risk of disease with others (Stefanska et al.,2012).
On the other hand, some studies have found evidence of increased disease severity and duration in infants infected with RSV and other respiratory viruses with similar seasonal distributions, such as influenza. As for COVID-19, several experiments on animals have identified an association between coinfections, increased pathogenicity, prolonged infection, and a higher risk of complications. For instance, Kim et al. (2022) have found that mice coinfected with SARS-CoV-2 and influenza A virus (IAV) exhibited increased mortality, prolonged viral shedding, and reduced levels of neutralizing antibody response compared to those with a single infection. Likewise, Kinoshita et al. (2021) have demonstrated that coinfection with the influenza A virus (IAV) causes more severe weight loss and more severe and prolonged pneumonia in SARS-CoV-2-infected hamsters.
What can you do to protect yourself this flu season?
Vaccination is our most effective strategy for the prevention of severe disease and complications associated with COVID-19 and influenza, regardless of whether it is a single infection or a coinfection. Staying up to date with COVID-19 vaccines and boosters is advised to all in order to boost the waning immunity against SARS-CoV-2 and reduce the risk of severe disease. Especially people with low or compromised immunity, those with underlying health conditions, and other groups which may be at higher risk of developing severe disease from infection with influenza viruses are also advised to receive the seasonally updated influenza vaccines.
Testing is another crucial aspect of disease control and prevention. The differentiation of infections and coinfections with common respiratory viruses may be challenging. Especially for hospitalized patients and severe infections observed in children, older adults, and immunocompromised patients, the simultaneous detection of multiple viral agents may be more efficient and reliable. Multiplex assays, such as our SARS-CoV-2 + Flu A/B + RSV Combo Rapid Test Kit, assist in diagnosing patients demonstrating respiratory disease symptoms through the differentiation of multiple infections and the detection of a possible coinfection.
REFERENCES
Kim, D., Quinn, J., Pinsky, B., Shah, N. H., & Brown, I. (2020). Rates of Co-infection Between SARS-CoV-2 and Other Respiratory Pathogens. JAMA, 323(20), 2085. https://doi.org/10.1001/jama.2020.6266
Kim, E. H., Nguyen, T. Q., Casel, M. A. B., Rollon, R., Kim, S. M., Kim, Y. I., Yu, K. M., Jang, S. G., Yang, J., Poo, H., Jung, J. U., & Choi, Y. K. (2022). Coinfection with SARS-CoV-2 and Influenza A Virus Increases Disease Severity and Impairs Neutralizing Antibody and CD4+ T Cell Responses. Journal of Virology, 96(6). https://doi.org/10.1128/jvi.01873-21
Kinoshita, T., Watanabe, K., Sakurai, Y., Nishi, K., Yoshikawa, R., & Yasuda, J. (2021). Co-infection of SARS-CoV-2 and influenza virus causes more severe and prolonged pneumonia in hamsters. Scientific Reports, 11(1). https://doi.org/10.1038/s41598-021-00809-2
Klein, E. Y., Monteforte, B., Gupta, A., Jiang, W., May, L., Hsieh, Y., & Dugas, A. (2016). The frequency of influenza and bacterial coinfection: a systematic review and meta‐analysis. Influenza and Other Respiratory Viruses, 10(5), 394–403. https://doi.org/10.1111/irv.12398
Stefanska, I., Romanowska, M., Donevski, S., Gawryluk, D., & Brydak, L. B. (2012). Co-Infections with Influenza and Other Respiratory Viruses. Advances in Experimental Medicine and Biology, 291–301.
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Zhu, X., Ge, Y., Wu, T., Zhao, K., Chen, Y., Wu, B., Zhu, F., Zhu, B., & Cui, L. (2020). Co-infection with respiratory pathogens among COVID-2019 cases. Virus Research, 285, 198005. https://doi.org/10.1016/j.virusres.2020.198005
