Eden’s team traced the types of RSV-A back to early 2020,concluding their origins were “a 50-50 call”:they either mutated within Australia or entered from abroad when tens of thousands returned home as Australia prepared to close its borders and became localised due to state border closures.
Although modellers predicted RSV would return after lockdown in larger numbers due to children not having immunity from previous exposure,it was assumed this would occur during winter. The summer wave of infections,also seen in parts of Europe and Israel,was a surprise.
“It was something we had never seen before,” Eden said,noting there wasn’t a spike in cases last summer possibly due to high COVID-19 transmission at the start of the year. “Viruses tend to suppress each other a little bit;they get in each other’s way.”
ANU infectious diseases physician and microbiologist Professor Peter Collignon said the past two years had revealed a lot about the behaviour of respiratory viruses.
“RSV never went away,but influenza is interesting because it really looks like we import it all,and now it is occurring earlier and with bigger numbers than a few years ago,” he said,adding he had previously assumed influenza existed at undetected community levels during the summer.
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Collignon said the winter surge in respiratory infections would probablyhave a greater impact on children than previous seasons,with reduced immunity due to lower virus rates for the past two years.
Children and teenagers have comprised more than half of this year’s influenza cases in NSW,which is experiencing an early flu season.
From Wednesday,flu shots will be free for all NSW residents,after the state-funded vaccines for those not included in the federal program.
As pandemic restrictions in NSW have eased,data shows cases of RSV as well as other respiratory infections,including rhinovirus and parainfluenza,are all increasing.
There were 1140 RSV cases confirmed by a PCR test in the week ending May 22,up from 766 the previous week and 508 the week before that,according to NSW Health’s respiratory surveillance reports.
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About 930 children under five presented at hospital with bronchiolitis,a lung infection generally caused by RSV,in May,with about 40 per cent admitted.
Eden is undertaking a genomic analysis of the recent wave of RSV cases,and expects both increased social mixing and the reopening of international borders are driving infections.
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