After the pandemic eased (and people practiced less social distancing and masking) came a huge surge in respiratory viral infections among young children, associated with significantly more morbidities. Many children were getting respiratory viruses even outside the typical “flu season.” One plausible reason for this surge is that SARS-CoV-2 had weakened children’s immune systems, making the children more susceptible to subsequent infections by respiratory viruses.
Another possibility is that children were not exposed to pathogens during the height of the pandemic as much as they were in earlier years. Since people were isolated and masking, children’s immune systems may have had less chance to build natural immunities to respiratory viruses.
Dr. Suchitra Rao, an associate professor of pediatrics at the University of Colorado Anschutz School of Medicine, recently led a team of doctors and scientists to understand the surge in respiratory viruses among children after the height of the pandemic. They asked whether children infected by SARS-CoV-2 were at greater risk of subsequent respiratory infections by reviewing electronic health records in two large cohorts of children: one cohort with over 70,000 children, and another with almost 145,000 children. Using these data, the team compared the risks of subsequent respiratory infections for children infected by SARS-CoV-2, children infected by influenza, and children infected by some other respiratory virus.
Strikingly, the team found that the odds of respiratory viral infections for children infected with SARS-CoV-2 were actually lower than or the same as they were for children infected by influenza; and lower than they were for children infected with some other respiratory virus. (Also noteworthy was that the odds of subsequent respiratory viral infections were greater for children who had been hospitalized for their first infections, for children with at least one high-risk medical condition, and for Black children.)
These results are striking because they contradict earlier studies reporting that SARS-CoV-2 infection increases risk of later infections. The research team suggested that critical differences in how data were analyzed may account for the different conclusions. For example, when measuring the odds of children first being infected by SARS-CoV-2 (or influenza) and then later being infected by respiratory viruses, the research team considered distinct “seasonalities” of the viral infections. Infections by influenza and other respiratory viruses (like RSV) have the same seasonality; they peak during the same months. In contrast, infections by SARS-CoV-2 happen more steadily throughout the year (without prominent seasonality).
Because some earlier studies did not consider overlapping seasonality, these studies may have overestimated correlations caused by infection by one virus increasing the chance of infection by another. Similarly, the research team was careful to avoid cases where children were simultaneously infected by both SARS-CoV-2 and a respiratory virus.
In contrast, earlier studies may have confused cases of co-infection with cases of sequential infections. Overall, this study highlights the importance of considering viral seasonality and rates of coinfections when determining risks of sequential viral infections.
Despite these strengths, the research team suggested ways to improve their analyses even more. First, using electronic health records to document infections by SARS-CoV-2 or respiratory viruses is challenging because these records lack information from at-home or outpatient diagnostic tests. Second, symptoms of respiratory viral infections can seem like symptoms of SARS-CoV-2 infection. Because these symptoms overlap, it can be difficult to tell whether children have subsequent infections by other viruses or whether they have lingering symptoms of their first infections. (However, the team partly addressed this concern by looking at cases where a long time passed between SARS-CoV-2 symptoms and symptoms of later infections.)
Also complicating analyses was variability in exposures. Some children had more exposure to respiratory viruses because they interacted with more children (e.g., at home or at daycares), and other children had less exposure because they interacted with fewer children.
This study was part of the NIH RECOVER program. The research team included doctors and scientists at Children’s Hospital of Philadelphia, Cincinnati Children’s Medical Center, Intermountain Health, NYU Grossman School of Medicine, St. Jude Children’s Research Hospital, and the University of Missouri School of Medicine. Also part of the team was Emily Taylor, Solve CEO.
Read the study here.
