Updated on Feb. 26, 2018.
Yes, it appears to have. About 6.4 percent of Americans visiting doctors in the week ending February 17 had flu symptoms, down from a peak of 7.7 percent two weeks before.
Flu activity was rated “high” in 39 states, as well as in New York City, the District of Columbia and Puerto Rico. Five states reported “moderate” activity. Six states are experiencing only “low” or “minimal” activity: Florida, Idaho, Washington, Maine, Montana and North Dakota.
It has been as bad as any since the Centers for Disease Control and Prevention adopted stringent surveillance methods in the early 2000s. The peak infection rate equaled that of the 2009 “swine flu” pandemic. (The rate is a measure of what percentage of all patients visiting doctors in a particular week had flulike symptoms, including a fever of at least 100 degrees.)
Even more worrying, the hospitalization rate for flu at one point was the highest the C.D.C. has ever recorded. It substantially surpassed that of the lethal 2014-2015 season, during which 710,000 Americans were hospitalized and 56,000 died.
Dr. Anne Schuchat, acting director of the C.D.C., said on Feb. 9 that the season was “on track to break some recent records.” (History’s worst influenza pandemics — in 1918, 1957 and 1968 — all occurred before the C.D.C.’s new surveillance standards were rolled out in the early 2000s and modified in 2010.)
It is too early to know how many Americans will ultimately die of this flu this season, but 9.5 percent of all deaths being recorded now are from flu or pneumonia, and a total of 97 children have died thus far.
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. As of Feb. 17, about 71 percent of all samples genetically sequenced have been H3N2, according to the C.D.C. That strain first emerged in Hong Kong in 1968 and killed an estimated 1 million people around the world that year. B strain flus are now becoming more common; in the last week of testing, more than a third of samples were B’s.
Some hospitals in some states, such as Texas, are struggling to keep up with a torrent of flu patients coming in. Local shortages of antiviral medications and flu vaccines have been reported, and patients may have to call several pharmacies to find shots or to fulfill prescriptions.
Hospitalization rates are leveling off, but the figures presage high death rates. As happens every season, some apparently healthy people have died. They include 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. The latest C.D.C. figures indicate that 97 children and teenagers have died of flu and its consequences, including pneumonia, meningitis and sepsis. In 2014-2015, 148 children died by flu season’s end.
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. More than 80 percent of those deaths are usually 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. This year, Americans aged 50 to 64 — part of the baby boom generation — are being hospitalized at unusually high rates, for reasons that are still unclear.
Its H3N2 component is a bad match for the circulating strain. On February 15, the C.D.C. released a preliminary estimate that it prevented infection with that strain 25 percent of the time.
In children under age 8, it did surprisingly well, working 51 percent of the time, the C.D.C. said. But in children aged 9 to 17, it appeared almost totally ineffective, for reasons that are unclear but might be related to previous recent vaccinations, a C.D.C. epidemiologist said. In adults, the vaccine was 12 percent to 20 percent effective.
Even 25 percent overall was better than the 10 percent efficacy rate reported in Australia, which had a severe 2017 flu season with many deaths. In Australia, flu vaccination is urged for only the most vulnerable, while in the United States millions of healthy people are vaccinated, which boosts apparent efficacy rates.
B strains are increasing, and the C.D.C. has found the vaccine to be 42 percent effective against them.
Experts say yes, because even when the shot does not prevent you from catching the flu, it may save you from dying of it.
On Monday, a different C.D.C. study looking back at the medical records of the 675 children who died of flu between 2010 and 2016 found that two-thirds of them had not had a flu shot. Children under age 2 were the most likely to die; children must be six months old before they can have a flu shot.
Because some doctors and pharmacies are out of vaccine, the C.D.C. suggests consulting vaccinefinder.org.
Yes, to the extent that they ever do. Of all the samples tested so far by the C.D.C., only 1 percent were resistant to oseltamivir, zanamivir and peramivir, the active ingredients in Tamiflu, Relenza and Rapivab. But to be effective, these medicines should be taken within 48 hours after symptoms appear.
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