\nScientific American<\/p>\n
![\"Flu](\"https:\/\/static.scientificamerican.com\/sciam\/assets\/Image\/2021\/fluUpdate_graphic_d.png\")
<\/picture><\/div>Since the novel coronavirus began its global spread, influenza cases reported to the World Health Organization have dropped to minuscule levels. The reason, epidemiologists think, is that the public health measures taken to keep the coronavirus from spreading also stop the flu. Influenza viruses are transmitted in much the same way as SARS-CoV-2, but they are less effective at jumping from host to host.<\/p>\n
As\u00a0Scientific American<\/em>\u00a0reported last fall<\/a>, the drop-off in flu numbers was both swift and universal. Since then, cases have stayed remarkably low. \u201cThere\u2019s just\u00a0no<\/em>\u00a0flu circulating,\u201d says Greg Poland, who has studied the disease at the Mayo Clinic for decades. The U.S. saw about 600 deaths from influenza during the 2020\u20132021 flu season.\u00a0In comparison, the Centers for Disease Control and Prevention estimated there were\u00a0roughly 22,000 deaths\u00a0in\u00a0the prior season and 34,000 two seasons ago.<\/p>\n Because each year\u2019s flu vaccine is based on strains that have been circulating during the past year, it is unclear how next year\u2019s vaccine will fare, should the typical patterns of the disease return. The WHO made its\u00a0flu strain recommendations for vaccines<\/a>\u00a0in 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\u20132022 vaccine will prove extra effective.<\/p>\n Public health experts are grateful for the reprieve. Some are also worried about a lost immune response, however. If influenza subsides for several years, today\u2019s toddlers could miss a chance to have an early-age response imprinted on their immune system. That could be good or bad, depending on what strains circulate during the rest of their life. For now, future flu transmission remains a roll of the dice.<\/p>\n The World Health Organization tracks influenza transmission in 18 zones. Three of those regions appear here. Only people who get tested for influenzalike illnesses\u2014typically about 5\u00a0percent of individuals who fall ill\u2014are tallied.<\/p>\nINFLUENZA CASES WORLDWIDE, BY REGION<\/h2>\n
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