How bad is this flu season?
At the moment, the 2017-2018 flu season is considered “moderately severe.” Large numbers of Americans have fallen ill, and every state except Hawaii has reported widespread flu activity. But some regions have been hit harder than others. More important, the number of people hospitalized or dying from flu nationwide is not unusually high. This season is closely paralleling the 2014-2015 season, which was dominated by the same H3N2 flu strain and was also “moderately severe.”
Is this year’s flu strain unusually dangerous?
H3N2 is the most dangerous of the four seasonal flu strains, but it is not new nor uniquely lethal. A typical season mixes two Type A strains — H1N1 and H3N2, and two Type B strains — Victoria and Yamagata. (The B strains normally arrive later and are rarer.) As of Jan. 7, about 78 percent of all samples genetically sequenced have been H3N2, according to the Centers for Disease Control and Prevention. That strain first emerged in Hong Kong in 1968 and killed an estimated 1 million people around the world that year. But it has circulated ever since, constantly undergoing small mutations. Many people have had it, and a weakened H3N2 strain is a component of every season’s flu shot, so partial immunity is widespread.
How many people are ill, and how do we know?
Almost 6 percent of all Americans seeking medical care now have flu symptoms. That is tracked by the C.D.C.’s Outpatient Influenza-like Illness Surveillance Network, to which about 2,000 doctors’ offices and clinics around the country report weekly how many of their patients have fevers of at least 100 degrees plus a cough or sore throat. The 2014-15 and 2012-13 flu seasons also peaked at close to 6 percent. By contrast, the mildest recent season, 2011-2012, barely surpassed 2 percent. In 2009, during the H1N1 “swine flu” pandemic, almost 8 percent of visits were flu-related, but they peaked in October, not in January. That never happens in seasonal flu but is typical of pandemic flus.
Are hospitals overwhelmed?
In some places, including Southern California and central Texas, some hospitals have seen so many flu patients that they had to set up triage tents or turn other patients away. But overall there have not been reports of regional shortages of antiviral medications, patients dying because a city ran out of respirators, or other signs of a major crisis.
Where is the flu spreading?
This year’s outbreak began in Louisiana and Mississippi, then spread across Texas to California and up the West Coast from San Diego to Seattle. It also stretched into the Midwest. Kinsahealth, which makes internet-connected thermometers and builds its database from 25,000 daily fever readings, says the current hot spot is the St. Louis area. The Northeast has been largely spared so far, as have Minnesota, the Dakotas and some Rocky Mountain states.
Are large numbers of people dying?
No, although it may appear so right now. The deaths of a few apparently healthy people — notably those of a 21-year-old fitness buff in Latrobe, Pa., a mother of three in San Jose, Calif., and a 10-year-old hockey player in New Canaan, Conn. — have been widely publicized, and some areas, like San Diego, have reported record numbers of deaths. But it is still too early to say how high mortality will be nationally. It can take weeks to confirm all flu-related deaths. As of now, the mortality rate for victims under age 18, a bellwether C.D.C. category, is well below that seen in the 2014-15 season.
How many usually die?
Even in a mild year, flu kills about 12,000 Americans, the C.D.C. estimates. In a bad year, it kills up to 56,000. Most of those deaths are among the elderly, but flu also kills middle-aged adults with underlying problems like heart or lung disease, diabetes, immune suppression or obesity. It is also dangerous for pregnant women, children under age 5 and children with asthma. And, every season, flu and its complications, including pneumonia, meningitis and sepsis, kill some apparently healthy people.