Clinical outcomes of SARS-CoV-2 coinfection with influenza viruses, respiratory syncytial virus, or adenoviruses

By Dr. Liji Thomas, MDReviewed by Danielle Ellis, B.Sc.Mar 29 2022

The ongoing pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections has caused hundreds of millions of documented cases of coronavirus disease 2019 (COVID-19), with over six million deaths so far. In response to the high transmissibility and large proportion of asymptomatic infections, public health strategies involved non-pharmaceutical interventions (NPIs) such as mask use in public, social distancing, and lockdowns.

A recent paper examines the occurrence of other respiratory viral infections during this period in patients already infected with SARS-CoV-2.

Introduction

As the pandemic seems to be on the wane, at least temporarily, it is recognized that other respiratory infections are likely to rebound from their extremely low rates of incidence to pre-pandemic levels. This is because NPIs aimed at reducing the transmission of SARS-CoV-2 will also decrease the spread of these other endemic viral pathogens.

Conversely, with the relaxation of such restrictions, these other viruses will probably begin to circulate again, along with SARS-CoV-2, leading to a rise in coinfections. The current study, published in The Lancet, aims to shed light on the outcomes of such coinfections.

What did the study show?

The investigators explored over 200,000 cases of SARS-CoV-2 infection among adults in the UK. The study was carried out between February 6^th, 2020, and December 8^th, 2021. In almost 7,000 cases, the patients were tested for concomitant influenza, respiratory syncytial virus (RSV), or adenovirus infections, with approximately 580 positive tests.

Among these, about 230 also had influenza, 220 had RSV, and 135 had adenovirus infections along with SARS-CoV-2. Patients with influenza virus coinfection had higher chances of requiring invasive mechanical ventilation (IMV) than those with SARS-CoV-2 infection alone.

In all cases of influenza and adenovirus coinfection, a fatal outcome was more likely. When the results were applied to hospitalized patients, in general, using appropriate adjustments, the presence of influenza was found to be a risk factor for IMV as well as death during the hospital stay.

What are the implications?

This is the largest study so far of adult patients with COVID-19 who were also tested for other endemic respiratory viruses. The participants included over 580 patients with such coinfections, identified over a period of 18 months.

Since the patients in the study were all hospitalized, the role played by the severity of COVID-19 in predisposing to testing for coinfections with other respiratory viruses must be accounted for. Despite this, the presence of influenza coinfection continued to be significantly associated with a higher risk of IMV than SARS-CoV-2 infection alone. This was not true of adenovirus or RSV coinfection when compared either to coinfection with influenza/SARS-CoV-2 or coinfection with SARS-CoV-2 alone.

Most of the cases of respiratory virus coinfection are assumed to have been due to community transmission and to have been present when the patient was hospitalized. However, the major part of the study occurred before the advent of COVID-19 vaccines, indicating the effect of the influenza virus or the COVID-19 vaccine on the outcome, whether in those with SARS-CoV-2 monoinfection or those with SARS-CoV-2 coinfection.

The study findings thus add to the sum of knowledge about the outcomes for hospitalized COVID-19 patients with influenza, adenovirus, or RSV coinfection.

The expected rise in the number of respiratory virus coinfections with the relaxation of measures to contain the transmission of SARS-CoV-2 further emphasizes the need for the flu shot as well as the COVID-19 vaccine. Secondly, the need to detect the presence of flu in hospitalized patients with COVID-19 may suggest that testing is a good way to identify those at risk.