Omicron variant resembles other respiratory viruses, posing challenges for syndromic surveillance

In a recent article published in Scientific Reports, researchers describe the symptom profiles of respiratory viral infections from the Flu Watch Community and the Virus Watch cohort studies to compare the frequency of the range of symptoms experienced during influenza, respiratory syncytial virus (RSV), rhinovirus, seasonal coronaviruses (CoVs) infections, and infections from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) wild-type (wt) strain and variants of concerns (VOCs), including Alpha, Delta, Omicron BA1/BA2/BA5.

Study: Symptom profiles of community cases infected by influenza, RSV, rhinovirus, seasonal coronavirus, and SARS-CoV-2 variants of concern. Image Credit: KitjaKitja/Shutterstock.com

Introduction

The study also evaluated how coronavirus disease 2019 (COVID-19) symptoms have changed with the advent of new SARS-CoV-2 variants and whether World Health Organization (WHO) definitions of influenza-like illness (ILI) and acute respiratory infection (ARI) could help identify the causal respiratory virus in people with symptomatic disease.

WHO defines ARI as the sudden onset of symptoms with cough, sore throat, runny nose, and ILI as fever ≥38 °C and cough.

Background

Respiratory viruses suppressed during the COVID-19-induced pandemic have started re-circulating globally with SARS-CoV-2 worldwide, with the suspension of non-pharmaceutical interventions (NPIs).

The United States of America (USA) Centre for Disease Control and Prevention (CDC) estimated that flu-related hospitalizations and deaths surpassed those of the past year.

Previous studies qualitatively compared the symptoms of SARS-CoV-2 with other respiratory viruses but did not quantitatively assess the symptom profiles of infected individuals.

About the study

In the present study, researchers restricted SARS-CoV-2 cases to those submitted by participants who met the WHO definition for ARI and presented symptom profiles of 10986 individuals with confirmed SARS-CoV-2 infection. 

Likewise, they gathered data on 191 seasonal CoV, 222 influenza, 84 RSV, and 283 rhinovirus cases from Flu Watch Community and the Virus Watch cohort studies to compare the proportion of symptoms experienced during both illnesses.

The Flu Watch study was conducted in entire households across England between 2006 and 2011, where the researchers analyzed the collected nasal swab samples for influenza infection, and to a lesser extent and at different times, for rhinovirus, RSV, and seasonal CoVs.

Another household community cohort study, Virus Watch, was conducted in England between 2020 and 2022 to analyze respiratory, constitutional, gastrointestinal, ocular, or skin symptoms self-reported by its participants through online surveys.

The team ran multiple multivariate logistic regression models to describe the odds of experiencing different respiratory and constitutional symptoms by SARS-CoV-2 VOCs.

However, primary exposure was by SARS-CoV-2 wt strain or VOCs with Omicron BA5 as the reference variant. They controlled for all known confounders, such as gender, age, clinal vulnerability status, and natural- or vaccine-induced immunity.

Results

With the advent of new SARS-CoV-2 VOCs, the SARS-CoV-2 symptomatology began to resemble other respiratory viruses. Thus, respiratory symptoms due to more contagious Omicron strains included increased coughing and sneezing.

It could contribute to their increased transmissibility compared to previous variants, as coughing and sneezing are modes for expelling viral particles. 

With Omicron BA2/BA5 variants emerging, SARS-CoV-2 illnesses meeting the WHO ARI case definition increased by +10 percentage points. 

This growing resemblance between SARS-CoV-2 symptoms with other respiratory illnesses, e.g., influenza infections, could make syndromic surveillance less effective, thus raising the need for multi-pathogen virological surveillance.

In addition, there will be a need for more accurate diagnostic tests to delineate influenza and SARS-CoV-2 infections, especially among high-risk patients considered for antiviral therapy.

Several previous studies have compared the symptoms of SARS-CoV-2 variants, including Omicron subvariants. The current study findings, however, provide additional information about Omicron BA5 symptomatology.

The authors noted that respiratory symptoms significantly increased with the spread of the Omicron VOCs. However, it remains unclear whether the observed change in symptomatology was due to the variant or changing immunity levels across the population. 

Before the emergence of Omicron, widespread COVID-19 vaccination and natural infections induced immunity in the general population; perhaps, it affected the symptomatology of respiratory viral infections.

Conclusions

The current study spans multiple years to facilitate the comparison of all SARS-CoV-2 VOCs that emerged during the same seasons and compare their symptomology with other common respiratory viruses.

It is important considering that the characteristics of respiratory virus infections vary significantly across seasons and regions due to their different variants, and that typically has varying effects on symptomatology.

For example, strains of influenza or any other respiratory virus currently circulating in the UK might have different characteristics than the ones predominant during 2006–2011. 

Even though no data suggested a significant change in influenza symptom profiles over these years in the UK, untangling the complex connections between symptomatology, immune mechanisms, and viral evolution could help elucidate the transmission advantages associated with more recent variants of all respiratory viruses.

Written by

Neha Mathur

Neha is a digital marketing professional based in Gurugram, India. She has a Master’s degree from the University of Rajasthan with a specialization in Biotechnology in 2008. She has experience in pre-clinical research as part of her research project in The Department of Toxicology at the prestigious Central Drug Research Institute (CDRI), Lucknow, India. She also holds a certification in C++ programming.