[10] The mechanism at play here has been suggested to be the expression of interferon-stimulated genes in the "target tissue" of HRV infection — the epithelium of the airway, where there has been observed to be an "unexpected high prevalence" of the virus, even among asymptomatic individuals.
[10] This potential interplay between viruses such as HRV and influenza may be one factor contributing to the timing and severity of their separate though overlapping "seasons".
The pandemic virus quickly became the dominant strain of influenza, largely displacing the seasonal ones in many countries; however, complete replacement was not observed.
[19] Despite the rapid spread around the world through the middle of the year, the pandemic remained in a lull during the summer in the north following an explosive outbreak in the spring.
[20] As predicted, the virus returned in epidemic proportions in the fall, earlier than the typical flu season but at a time when respiratory illnesses are known to become more prevalent.
This difference was attributed by some observers to a rhinovirus epidemic that broke out upon the reopening of schools, effectively "delaying" the rise in H1N1 cases until October.
[24] While this "delay" in countries like Sweden was real (i.e., temporally speaking, the epidemic was later than in other places), studies also showed that coinfections were relatively common and that there was active cocirculation of the two viruses.
[30] By contrast, cases of HRV and respiratory enteroviruses declined at the onset of the pandemic but soon returned to prepandemic levels, circulating relatively normally.
[32] A similar phenomenon was observed in Hong Kong in March 2022, when other respiratory viruses "disappeared" during the surge before returning in April.
[17] With respect to HRV and respiratory enteroviruses, whose behavior was evidently less affected during the pandemic, an apparent interplay between these and SARS-CoV-2, possibly mediated by viral interference, was identified in some places, such as California and South Korea.