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A a curious thing happened when Hong Kong reopened schools after closing them due to the Covid-19 pandemic. It is worth looking here.
Hong Kong closed its schools to in-person learning from late January 2020 to late May – then again in early July, when more cases of Covid were detected. Weeks after schools reopened in October, they began to see large numbers of children falling ill, despite mandatory masks, extra space between desks and other measures to reduce the risk of the spread. of SARS-CoV-2, the virus. which causes Covid-19.
But the children were not infected with the virus. They also didn’t have the flu, which would have been another possibility. They got infected with rhinoviruses – one of the most common causes of colds.
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Researchers believe the rise in the disease is not an accident – but rather a consequence of children coming together after so many months of social distancing. In short, they may have been more susceptible to respiratory viruses because they were likely less exposed to people outside their home and therefore less likely to contract them and develop immunity.
The results were recently published in Emerging Infectious Diseases, the journal of the Centers for Disease Control and Prevention.
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“I imagine places where schools have been closed for a long time are going to have the same experience as Hong Kong,” said Ben Cowling, professor of infectious disease epidemiology at the University of Hong Kong and lead author of the report. “That when the schools come in, suddenly there will be a lot of rhinoviruses circulating, a lot of kids get sick with the common cold, and then their parents throw it off and panic thinking it could be Covid.”
A number of viruses that cause colds and flu illnesses have disappeared since Covid-19 began to spread widely around the world. There was virtually no influenza activity during the southern hemisphere winter in July and August; So far this winter, only about 1,400 people in the United States have tested positive for the flu. At the same time last year, more than 174,000 people had tested positive for the flu – more than a hundred times the difference. And around the same time last year, 105 children had died from the flu in the country; this year, this tragic toll is attributable to one child.
(Flu cases diagnosed by a test are the tip of the iceberg, even in normal season.)
Likewise, infections caused by respiratory syncytial virus, or RSV, are on the decline. RSV causes a cold-like illness that is normally mild; but in young children and older adults the infection can be severe. In a typical year, about 58,000 children under five are hospitalized with RSV and about 14,000 adults over 65 die from it.
Rhinoviruses, on the other hand, mainly cause mild colds; the more than 200 viruses of the rhinovirus family are estimated to be responsible for about a third of all colds. And, while the Hong Kong experience is any indication, it does not appear to be contained by the measures in place to minimize the spread of Covid.
A total of 482 rhinovirus outbreaks were reported by schools over a period of approximately one month, from late October to late November. The vast majority were in elementary schools, kindergartens, preschools and nurseries.
“The susceptibility of the population to rhinoviruses and other respiratory viruses, including influenza viruses, may have increased over time because people were likely less exposed to viruses when intense social distancing measures, including school dropouts, have been implemented in response to the Covid-19 pandemic, ”the authors of the new article wrote. “It would have increased the potential for transmission to take over schools.”
The authors, who are all from the University of Hong Kong, noted that a similar phenomenon was observed by British researchers, who reported a sharp increase in rhinovirus infections in adults beginning about two weeks after returning from children at school in the UK last September.
Cowling and his colleagues previously reported that the amounts of human coronaviruses and influenza viruses emitted by infected people are significantly reduced if they wear surgical masks, but the same is not true for rhinoviruses. This and the fact that rhinoviruses are resistant – they may withstand surface cleaning better than coronaviruses and influenza viruses – may help explain why they continue to circulate while other respiratory viruses have declined in incidence, have said the researchers.
Covid control measures likely do not fully explain the phenomenon, said Ed Belongia, director of the Center for Clinical Epidemiology and Population Health at the Marshfield Clinic in Wisconsin.
Belongia noted that during the 2009 H1N1 influenza pandemic, seasonal influenza viruses and RSV virtually disappeared for some time, although masks were not common outside parts of Asia to back then and that many social distancing tools currently in use were not among them. of the response to the pandemic.
“We don’t really understand what’s going on here in terms of these different patterns of viral circulation. We obviously don’t have a lot of experience with pandemics and what pandemics do to the circulation of other viruses, ”Belongia said.
Researchers in Hong Kong noted that not only were there a lot of rhinovirus cases, but there were more serious infections than is normally seen, with some of the children needing hospital care.
“It seemed to be more than usual,” Cowling said. “I think it’s to do with this loss of immunity. Not only were the children much more sensitive, but maybe they were more sensitive. “
The same phenomenon could happen with the flu when influenza viruses start to circulate again, Cowling and others warn. Lack of exposure to influenza viruses for more than a year could make many people more susceptible to viruses when Covid containment measures are relaxed.
“If I were to bet on this, then I guess we’ll probably have a more serious outbreak over the next winter – assuming the restrictions are completely lifted by then,” John Edmunds of the London School of Hygiene and Tropical Medicine and a member of the UK government’s Sage Scientific Advisory Board, recently told the Daily Telegraph.
Cowling agreed. “Once the measures are relaxed, once people try to get back to normal, we’re going to have the biggest flu season on record,” he predicted.
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