The relaxation of the restrictions for Covid-19 could cause a strong rebound in cases of seasonal flu, which is why “getting the flu vaccine this year is particularly important”: the invitation is from Amer Winn, epidemiologist at the Division Viral Diseases of the US Centers for Disease Control and Prevention (the CDCs of Atlanta, Georgia).
And it is the synthesis of an article published in Nature, in which scientists substantially agree that the flu will return to strike, perhaps in a ferocious way, as travel restrictions and interventions aimed at curbing the Covid-19 (starting with the use of the mask).
The data speak for themselves. The United States recorded only 646 deaths from influenza in the 2020-21 season – the annual average is in the tens of thousands – and there has been only one death from pediatric influenza. So far Australia has had no deaths from seasonal flu in 2021 (in previous years it recorded between 100 and 1,200).
But the flu continued to circulate at low levels in the tropics and therefore – researchers note – it will probably start to recover from there once the borders are reopened. But there is more. Response measures to the pandemic appear to have suppressed some bacterial infections, including those that cause pneumonia and meningitis and are associated with sepsis.
But some viruses – for example rhinoviruses, one of the main causes of the common cold – have continued to circulate and infections have even increased in some countries, perhaps because they are viruses that are not as sensitive as others to precautionary measures such as surface cleaning and hand washing. Not only.
Infections caused by common human coronaviruses (another major cause of colds) and parainfluenza viruses were at very low levels in the United States in 2020, but began to rise again to pre-pandemic levels in the spring of 2021, an unusual time for colds.
Similarly, respiratory syncytial virus infections, which usually cause mild cold symptoms but are also responsible for about 5% of deaths in children under 5 worldwide, have been at an all-time low for a year and then began to rise, in April this year (according to the CDC these peaks could be linked to the reopening of schools).
Among other things around the world, there are signs of circulation of the influenza viruses H3N2, H1N1 and influenza B; and a wave of influenza B infections in the winter of 2019-20, in that same period contributed to a record number of deaths from pediatric influenza. “This is why – concludes Winn – getting the flu shot this year can be particularly important”.