ONE a curious thing happened when Hong Kong reopened schools after closing them because of the Covid-19 pandemic. It is worth watching here.
Hong Kong closed its schools for face-to-face learning from late January 2020 to late May – and again in early July, when more cases of Covid were detected. A few weeks after schools reopened in October, they began to see a large number of children falling ill, despite the mandatory use of a mask, additional wall spacing and other measures to reduce the risk of spreading the SARS-CoV-2 virus that causes Covid-19.
But the children were not infected with the virus. They didn’t even have the flu, which would be another possibility. They were infected with rhinovirus – one of the most common causes of the common cold.
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The researchers believe that the increase in disease was not accidental – but a consequence of the congregation of children after so many months of social detachment. In short, they may have been more susceptible to respiratory viruses because they were probably less exposed to people outside their homes and therefore less likely to contract them and develop immunity.
The findings were recently published in Emerging Infectious Diseases, the journal of the Centers for Disease Control and Prevention.
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“I can imagine places where schools have been closed for a long time will have the same experience as Hong Kong,” said Ben Cowling, professor of infectious disease epidemiology at the University of Hong Kong and senior author of the report. “That when schools come back, there will suddenly be a lot of rhinoviruses circulating, a lot of children getting a cold and then their parents taking it away and panicking because it could be Covid.”
A series of viruses that cause colds and flu-like illnesses have disappeared since Covid-19 began to spread widely around the world. There was virtually no flu 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 flu. At that time, last year, more than 174,000 people had tested positive for influenza – a difference of over a hundred times. And at this time last year, 105 children died of influenza in the country; this year, the tragic number has fallen for an only child.
(Flu cases diagnosed by a test are the tip of the iceberg, even in a normal season.)
Likewise, infections caused by the respiratory syncytial virus, or RSV, have decreased. RSV causes cold-like illnesses, which are usually mild; but in young children and older adults, the infection can be serious. In a normal 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; it is estimated that the more than 200 viruses of the rhinovirus family are responsible for about one third of all colds. And if the Hong Kong experience is any indication, they do not seem to be contained by the measures in place to minimize the spread of Covid.
In total, there were 482 outbreaks of rhinovirus reported by schools over a period of about a month, from late October to late November. The vast majority were in primary schools, kindergartens, daycare centers and daycare centers.
The “susceptibility of the population to rhinoviruses and other respiratory viruses, including influenza viruses, may have increased over time because people were probably less exposed to viruses when intense measures of social distance, including school leavers, were implemented in response to the pandemic. Covid-19, “wrote the authors of the new article.” This would have increased the potential for transmission when schools were resumed. “
The authors, all from the University of Hong Kong, noted that a similar phenomenon was observed by British researchers, who reported a marked increase in rhinovirus infections in adults from about two weeks after children returned to school in the UK in last september.
Cowling and his colleagues had previously reported that the amounts of human coronaviruses and influenza viruses emitted by infected people are greatly reduced if they are wearing surgical masks, but the same is not true for rhinoviruses. That and the fact that rhinoviruses are resistant – they may be better able to resist surface cleaning than coronaviruses and flu viruses – can help explain why they continue to circulate while other respiratory viruses have decreased in incidence, the researchers said.
Covid’s control measures are unlikely to fully explain the phenomenon, said Ed Belongia, director of the Center for Clinical Epidemiology and Population Health at the Wisconsin Marshfield Clinic.
Belongia noted that during the 2009 H1N1 flu pandemic, seasonal flu viruses and RSV practically disappeared for a while, although mask use was not common outside parts of Asia at that time and many of the tools of social detachment today in use were not part of the response to the pandemic.
“We really don’t understand what’s going on here in terms of these different patterns of virus circulation. Obviously, we don’t have much experience with pandemics and what pandemics do to the circulation of other viruses, ”said Belongia.
The Hong Kong researchers noted that not only were there many cases of rhinovirus, but there were also more serious infections than normally seen, with some of the children in need of hospital care.
“It seemed to be more than normal,” said Cowling. “I think it has to do with the loss of immunity. Not only were they more susceptible children, they were perhaps more susceptible. “
The same phenomenon can happen with the flu when flu viruses are circulating again, Cowling and others warn. Lack of exposure to influenza viruses for more than a year can make many people more susceptible to viruses when Covid’s containment measures are facilitated.
“If I had to bet on that, then I think we’ll probably have a more severe epidemic next winter – assuming restrictions are fully lifted by then,” John Edmunds of the London School of Hygiene and Tropical Medicine and a member of the Sage committee on British government scientific consultants, he told the Daily Telegraph recently.
Cowling agreed. “As soon as the measures are relaxed, when people try to return to normal, we will have the biggest flu season on record,” he predicted.