Worldwide influenza cases reported to the World Health Organization (WHO) have dropped to minuscule levels since the spread of Covid-19 pandemic.
Epidemiologists think the reason behind this is that public health measures taken to keep the coronavirus from spreading also stop the flu, according to an article in the Scientific American.
Influenza viruses are transmitted in much the same way as SARS-CoV-2, but they are less effective at jumping from host to host.
As Scientific American reported last fall,
The drop-off in flu numbers has been both swift and universal. Since then, cases have stayed remarkably low.
"There is just no flu circulating," said Greg Poland, who has studied the disease for decades at the Mayo Clinic, US.
The US saw about 600 deaths from influenza during the 2020-2021 flu season. In comparison, the Centers for Disease Control and Prevention estimated there were roughly 22,000 deaths in the prior season and 34,000 two seasons ago.
However, each year's flu vaccine is based on strains that have been circulating during the past year, it is unclear how next year's vaccine will fare, should the typical patterns of the disease return. The WHO made its flu strain recommendations for vaccines in late February as usual, but they were based on far fewer cases than in a common year.
At the same time, with fewer virus particles circulating in the world, there is less chance of an upcoming mutation, so it is possible the 2021–2022 vaccine will prove extra effective. Public health experts are grateful for the reprieve.
Some are also worried about a lost immune response, however. If influenza subsides for several years, toddlers from now-e-days could miss a chance to have an early-age response imprinted on their immune system. Depending on what strains circulate during the rest of their life - it could be good or bad.