The changing pattern of respiratory viruses during covid-19—what does the future hold?

Recognition of how the pandemic has altered the infectious rhythm of viruses can lead to better preparedness in the health community, write Rabia Agha and Jeffrey R Avner

As pediatricians, we are used to the typical seasonality of acute infectious illnesses in children: enteroviruses in the summer, parainfluenza in the fall, respiratory syncytial virus (RSV) in the fall/winter, followed closely by influenza.

Over the past year, the effect of the covid-19 pandemic has altered that infectious rhythm, due to social distancing, hand washing, masking, and perhaps even features intrinsic to the SARS-CoV-2 virus (e.g. the antiviral defense generated in the airways by one predominant virus can prevent other viruses from attaching and causing infection). These factors, taken together, led to an impressive decline of the usual viral pathogens during much of 2020 and early 2021. This trend was evident by a sharp decline in pediatric emergency department visits and inpatient pediatric admissions—a phenomenon noted in the US and reported globally. Still, knowing the resilience of infectious pathogens, it was just a matter of time until surges of seasonal viruses would return. We take a look at the shifting patterns of respiratory viruses that have been observed over the past year.      

Rhinoviruses are present all year round but there have been markedly fewer cases during much of the pandemic. Reports from Hong Kong documented an increase in upper respiratory infections, especially in childcare centers and primary schools, when schools reopened in October to November 2020. Most cases tested positive for rhinovirus despite the use of masks by staff members and students. It’s worth noting that rhinovirus transmission is not completely blocked by masks and the virus is relatively more resistant to disinfectants as it lacks an outer lipid coat or envelope. It is also more stable on surfaces, which allows it to spread via hands, doorknobs, desks, etc. Similar findings were noted in a UK study, which found that between March and August 2020, there was a lower number of rhinovirus infections in adults and children compared with the previous year’s data, before there was a sharp increase when schools reopened in September 2020. 

Various studies have suggested that infection with rhinoviruses may prevent other coronaviruses and possibly influenza virus by producing a strong immune response that competes with and prevents other viruses from setting in—a phenomenon known as viral interference. Various mechanisms have been proposed for this interference, including one virus blocking viral entry receptors for another, viruses competing for host cell resources, and one virus inducing an immune response that protects against other viruses.

RSV is typically a fall/winter virus. Infants and young children, as well as older adults with chronic medical conditions, are at high risk for severe RSV disease. RSV activity was very low in many countries during the fall/winter 2020 season due to public health restrictions in place to reduce covid-19 cases. An out of season, unexpected, acute increase of RSV cases was first reported from the southern hemisphere in Australia during their spring. They reported a higher than average number of cases and infections in older infants. We published our findings of an end of season surge in RSV infections noted at our hospital in New York, USA. The median age of the patients admitted to our hospital was younger than in the previous fall/winter season (6 months vs 17 months) and most required intensive care, which indicates the increased severity of cases. The US Centers for Disease Control and Prevention then published a health advisory notifying clinicians and caregivers of a similar out of season increase in RSV cases in the southern states of the US. France and Japan have reported similar findings. New Zealand, which is currently in its winter season, has already recorded in the first five weeks of this winter more than half the number of RSV cases that it saw each winter season over the previous five years. 

Our recognition of these unexpected patterns can lead to better preparedness in the health community, including more testing even if the typical season has passed, and prolongation of preventive measures, like palivizumab treatment for premature infants beyond the usual time frame of administration, as we did in our hospital.

Influenza is a predominant winter virus that generally coincides with or follows RSV seasonality. To date, however, we have not seen an influenza upsurge in countries after pandemic restrictions for covid-19 were eased. There is markedly decreased influenza activity reported in the southern hemisphere, which usually precedes that of the northern hemisphere. Nevertheless, it remains difficult to predict future influenza activity due to the variability of the influenza strain, diminished air travel, and the increase in annual vaccination against influenza at the onset of the covid-19 pandemic.

Our description of the epidemiology of some common circulating viruses during the covid-19 pandemic highlights how difficult it is to predict the pattern and infectivity of respiratory viruses in the upcoming months. Furthermore, given the unexpected late RSV season and the absence of infection in the prior season due to covid-19 restrictions, there will likely be a larger, more vulnerable group of children in the upcoming season. We know that vulnerable hosts tend to have worse disease. Therefore, we need to be vigilant in infection surveillance testing, be prepared to exercise control measures quickly, maintain good hygiene practices, and improve lapsed vaccination rates to counter any upsurge in viral illnesses. 

As with most infectious illnesses, the nature of the disease depends on the interaction between the organism and the host. As we’ve repeatedly seen during the covid-19 pandemic, an alteration to either one can lead to unexpected outbreaks. 

Rabia Agha, division director, pediatric infectious diseases, Maimonides Children’s Hospital, Brooklyn, NY, USA

Jeffrey R Avner, chair, Department of Pediatrics, Maimonides Children’s Hospital, Brooklyn, NY, USA

Competing interests: none declared.