The relaxation of anti-Covid measures could cause a sharp upsurge in cases of seasonal flu. Some respiratory viruses have continued to circulate at low levels in the tropics, experts say, and will return to circulation as international travel resumes.
The Covid-19 pandemic continues to have unusual and unexpected effects on a range of respiratory illnesses, such as the common cold and the seasonal flu. Data indicates that for most of 2020-2021, influenza was virtually extinct around the world. The United States recorded just 646 deaths from seasonal flu in 2020-2021, compared to an annual average of tens of thousands of deaths and a single death from childhood flu. Likewise, no flu deaths have been reported in Australia to date, compared to 100 to 1,200 deaths in previous years.
Some pandemic response measures appear to have suppressed some infections, including those that cause pneumonia and meningitis and are associated with sepsis, experts say. For seasonal influenza, this decline has continued despite varying levels of relaxation of social interventions, as noted in a publication in Nature, in which the authors agree that influenza viruses will return to circulate, perhaps more fiercely, with the resumption of international travel.
« This says a lot about their importance in importing influenza into a particular country and how critical these seeding events are.Said Richard Webb of St. Judde Childreen Research Hospital in Memphis, Tennessee. Influenza viruses have continued to circulate at low levels in the tropics and so likely – the researchers note – this is where they will circulate once borders are reopened.
However, other viruses behaved differently. Rhinoviruses, which are a major cause of the common cold, continued to spread throughout the pandemic. In some countries infections have even increased, perhaps because these viruses are not as sensitive to health measures as many others, or perhaps because they have faced little competition from other respiratory viruses. Some typical winter viruses have recovered out of season, with an increase in infections linked to common human coronaviruses (another cause of the common cold) and parainfluenza viruses, starting to reach pre-pandemic levels in the spring of 2021 in the United States, a situation unusual. cold period. Respiratory syncytial virus (RSV) infections, which usually cause mild symptoms of the common cold but are also responsible for around 5% of deaths of children under 5 worldwide, also began to increase later than d usual, in April 2021, and were still on the rise at the end of August 2021.
According to the United States Centers for Disease Control and Prevention (CDC), these rebounds could be linked to the opening of schools, with some infants susceptible and not yet exposed to the viruses, in the absence of vaccination (the RSV vaccines are under development). Out-of-season RSV peaks have also been seen elsewhere, in countries such as South Africa, Japan, Australia and the Netherlands. In Western Australia, RSV cases in December 2020 were 2.5 times higher than their peak in July 2019.
Among other things, all over the world, there are signs of the circulation of influenza viruses H3N2, H1N1 and influenza B and ” it would be worrying to see rebound effects caused by an accumulation of people immunologically never exposed to seasonal influenza“Researchers warn. ” A wave of influenza B infections in the winter of 2019-2020 – noted Amber Winn, epidemiologist at CDC’s Division of Viral Diseases in Atlanta, Georgia – contributed to a record number of pediatric flu deaths that season. That’s why getting the flu shot this season can be especially important.« .
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