The easing of anti-Covid measures could cause a sharp upsurge in cases of seasonal flu. According to experts, some respiratory viruses have continued to circulate at low levels in the tropics and will return to circulate as international travel resumes.
The Covid-19 pandemic continues to have unusual and unexpected effects on a range of respiratory diseases, such as the cold and seasonal flu. The data indicates that for most of 2020-21 the flu has virtually disappeared globally. The United States recorded only 646 deaths from seasonal flu in 2020-21, compared with an annual average of tens of thousands of deaths, and only one death from childhood flu. Likewise, no deaths from influenza have been reported to date in Australia compared to 100-1,200 deaths in previous years.
According to experts, some pandemic response measures appear to have suppressed some infections, including those that cause pneumonia and meningitis and are associated with sepsis. For seasonal flu, this decline has continued despite varying levels of easing of social interventions, as indicated in a publication in Nature, in which the authors agree that influenza viruses will return to circulate, perhaps more ferociously, with the resumption of international travel.
“This speaks volumes about their importance in importing influenza into a particular country and how decisive these seeding events are.Said Richard Webb of St. Judde Childreen’s Research Hospital in Memphis, Tennessee. Influenza viruses continued to circulate at low levels in the tropics and therefore probably – the researchers note – that is where they will circulate once the borders are reopened.
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However, other viruses have behaved differently. THE rhinovirus, 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 infection-related cases common human coronaviruses (another responsible for the cold) ea virus parainfluenzali, starting to rise to pre-pandemic levels in the spring of 2021 in the US, an unusual time for colds. Infections with virus respiratory syndrome (RSV), which usually causes mild cold symptoms, but is also responsible for around 5% of deaths in children under 5 worldwide, began to rise later than usual, in April 2021, and were still in increase at the end of August 2021.
According to the United States Centers for Disease Control and Prevention (CDC), these rebounds could be related to the opening of schools, along with part of susceptible and not yet exposed infants to the viruses, in the absence of vaccination (vaccines against RSV are undergoing of development). Out-of-season RSV peaks have also been observed elsewhere, in countries including South Africa, Japan, Australia and the Netherlands. In Western Australia, RSV cases in December 2020 were 2.5 times higher than their July 2019 peak.
By the way, all over the world, there are signs of circulation of influenza viruses H3N2, H1N1 and influenza B e “it would be worrying to see rebound effects caused by an accumulation of people immunologically never exposed to seasonal flu”The researchers warn. “A wave of influenza B infections in the winter of 2019-20 – noted Amber Winn, epidemiologist with the CDC’s Division of Viral Diseases in Atlanta, Georgia – contributed to a record number of pediatric influenza deaths that season. That’s why getting the flu shot this season can be especially important”.