SARS-CoV-2 co-infection with influenza, respiratory syncytial virus, or adenoviruses

March 31, 2022

Measures to reduce transmission of SARS-CoV-2 have also been effective in reducing the transmission of other endemic respiratory viruses, according to a news release.

As many countries decrease the use of such measures, researchers expect that SARS-CoV-2 will circulate with other respiratory viruses, increasing the probability of co-infections. The clinical outcome of respiratory viral co-infections with SARS-CoV-2 is unknown.

Researchers examined clinical outcomes of co-infection with influenza viruses, respiratory syncytial virus, or adenoviruses in 212 466 adults with SARS-CoV-2 infection who were admitted to hospital in the UK between Feb 6, 2020, and Dec 8, 2021, using the International Severe Acute Respiratory and Emerging Infection Consortium–WHO Clinical Characterization Protocol. Ethical approval was given by the South Central-Oxford C Research Ethics Committee in England, the Scotland A Research Ethics Committee, and the WHO Ethics Review Committee.

Tests for respiratory viral co-infections were recorded for 6965 patients with SARS-CoV-2. Viral co-infection was detected in 583 (8·4%) patients: 227 patients had influenza viruses, 220 patients had respiratory syncytial virus, and 136 patients had adenoviruses. Co-infection with influenzas viruses was associated with increased odds of receiving invasive mechanical ventilation compared with SARS-CoV-2 monoinfection. SARS-CoV-2 co-infections with influenza viruses and adenoviruses were each significantly associated with increased odds of death.

To extrapolate these results from the tested population to a representative hospitalized population, researchers accounted for differences between tested and non-tested patients using inverse probability weighting (table). In this weighted multivariable regression analysis, influenza virus co-infection significantly increased the odds of receiving invasive mechanical ventilation and the odds of in-hospital mortality.

As public health restrictions are lifted, respiratory virus co-infections are more likely to occur during future winters. The marked increase in risk among patients with co-infection has several implications for policy. First, results provide further support for vaccination against both SARS-CoV-2 and influenza viruses. Second, they suggest that testing for influenza viruses is important in hospital inpatients with COVID-19 to identify patients at risk and a cohort of patients who might have different responses to immunomodulatory and antiviral therapy.

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