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Influenza (Flu)

Calypta Health Disease Information Statement

Of 10,000 people who get the flu *

Under 5
~70 hospitalized, ~1 dies 9
5 to 17
~25 hospitalized, <1 dies 10
18 to 49
~55 hospitalized, ~2 die 11
50 to 64
~105 hospitalized, ~7 die 12
65+
~910 hospitalized, ~100 die 13

* Based on CDC estimates for a typical season, 2010 to 2025. 14

Of 10,000 people who get the flu shot

≪1 have a serious side effect, 0 die 15 , 19

A minor sore arm, aches, or fatigue for a few days is common. 20

≪1 means much less than one: a few per million each. 21

Disease Information Statement · Influenza (Flu) · 2026–27 season © 2026 Calypta Health
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Sources

Based on the versions of these sources published as of October 5, 2026.

  1. 1. A respiratory virus. In fall and winter, tens of millions of Americans get sick with it.

    CDC: flu is “a contagious respiratory illness caused by influenza viruses.” CDC estimates 9.4 million to 51 million symptomatic illnesses per season over the 14 estimated seasons from 2010–11 to 2024–25 (2024–25 preliminary); 13 of the 14 exceed 10 million. “Tens of millions” characterizes a typical season.

  2. 2. Can spread before symptoms start. Someone who feels fine can pass it on, including to people at high risk.

    CDC: flu virus is detectable in most infected people “beginning one day before symptoms develop,” and “some otherwise healthy adults may be able to infect others beginning one day before symptoms develop.” CDC’s list of people at higher risk of serious flu complications includes children under 5, adults 65 and older, pregnant women, and people with heart disease, asthma, or diabetes.

  3. 3. Causes fever, chills, body aches, and exhaustion. Usually a few days to two weeks of misery.

    CDC: symptoms include “fever or feeling feverish/chills,” “muscle or body aches,” and “fatigue,” and most people “will recover in a few days to less than two weeks.”

  4. 4. Heart disease, asthma, and diabetes make it more dangerous. Serious complications are more common.

    CDC: people with heart disease and people with diabetes “are at higher risk of developing serious flu complications,” and people with asthma “are more likely to have serious health problems from getting the flu.” In FluSurv-NET, about nine in ten adults hospitalized with flu had at least one underlying condition.

  5. 5. Pregnant women are at higher risk. Hospitalization is more likely; severe cases are linked to premature birth.

    CDC: “Influenza (flu) during pregnancy is more likely to cause illness that results in hospitalization.” Regan 2020 followed women hospitalized with flu: 11.6% delivered preterm, compared with 7.1% of matched controls. Pierce 2011 followed women hospitalized with 2009 H1N1: the adjusted odds of preterm birth were 2.5 times those of uninfected women.

  6. 6. Can trigger heart attacks. In the week after flu infection, heart attack rates are several times higher.

    Kwong 2018 counted hospital admissions for heart attack in “the first 7 days after respiratory specimen collection” from people with laboratory-confirmed flu: 20.0 per week, compared with 3.3 per week in the comparison intervals, an incidence ratio of 6.05 (95% CI 3.86–9.50). Young-Xu 2020 repeated the design in U.S. veterans and found an incidence ratio of 8.89 (95% CI 6.16–12.84).

  7. 7. Kills tens of thousands in most years. Mainly people 65 and older, but healthy children also die.

    CDC estimates: 6,300 to 52,000 deaths per season over the 14 estimated seasons from 2010–11 to 2024–25 (2024–25 preliminary), with deaths exceeding 20,000 in 12 of the 14. Over the 13 seasons that exclude the two COVID-19 seasons (2020–21, with no estimate, and 2021–22), the mean is about 34,000. Adults 65 and older account for “70–85% of seasonal flu-related deaths.” Among children who died of flu and whose medical history was known, 51% (96 of 189) had no underlying condition in 2023–24, and 44% (114 of 262) had no underlying condition in 2024–25.

  8. 8. The shot cuts the risk of flu by about 40% in a typical year. Those who catch it anyway tend to get less sick.

    CDC’s estimates of vaccine effectiveness for each season since 2010–11 range from 19% (2014–15) to 60% (2010–11), with a median of 40%. CDC: “During seasons when the influenza viruses used in flu vaccine production are similar to those that are spreading, studies show flu vaccination reduced the risk of a flu-related doctor’s visit by 40-60%.”

    Ferdinands 2021 reviewed observational studies of adults hospitalized with flu: vaccinated patients were less likely to be admitted to intensive care or to die, and vaccination “may attenuate the course of disease.” Thompson 2018 studied adults hospitalized with flu in New Zealand, adjusting for a vaccination propensity score: vaccinated patients “were 59% less likely to be admitted to the ICU” and had shorter ICU stays.

  9. 9. Under 5: ~70 hospitalized, ~1 dies

    According to CDC’s estimates for past flu seasons, 69.7 of every 10,000 children under 5 with flu symptoms are hospitalized. Deaths per 10,000 with symptoms average 0.73 (range: 0 to 1.35) across the 13 seasons from 2010–11 to 2024–25, leaving out the two COVID-19 seasons.

  10. 10. 5 to 17: ~25 hospitalized, <1 dies

    According to CDC’s estimates for past flu seasons, 27.4 of every 10,000 children and teens aged 5 to 17 with flu symptoms are hospitalized. Deaths per 10,000 with symptoms average 0.37 (range: 0 to 1.25) across the 13 seasons from 2010–11 to 2024–25, leaving out the two COVID-19 seasons.

  11. 11. 18 to 49: ~55 hospitalized, ~2 die

    According to CDC’s estimates for past flu seasons, 56.1 of every 10,000 adults aged 18 to 49 with flu symptoms are hospitalized. Deaths per 10,000 with symptoms average 2.07 (range: 1.14 to 6.94) across the 13 seasons from 2010–11 to 2024–25, leaving out the two COVID-19 seasons.

  12. 12. 50 to 64: ~105 hospitalized, ~7 die

    According to CDC’s estimates for past flu seasons, 106.0 of every 10,000 adults aged 50 to 64 with flu symptoms are hospitalized. Deaths per 10,000 with symptoms average 6.97 (range: 4.42 to 12.09) across the 13 seasons from 2010–11 to 2024–25, leaving out the two COVID-19 seasons.

  13. 13. 65+: ~910 hospitalized, ~100 die

    According to CDC’s estimates for past flu seasons, 909.1 of every 10,000 adults 65 and older with flu symptoms are hospitalized. Deaths per 10,000 with symptoms average 100.27 (range: 70.8 to 162.9) across the 13 seasons from 2010–11 to 2024–25, leaving out the two COVID-19 seasons.

  14. 14. Based on CDC estimates for a typical season, 2010 to 2025.

    The figures are averages over 13 flu seasons, 2010–11 through 2024–25, leaving out the two COVID-19 seasons. CDC has no estimate for 2020–21 “due to minimal flu activity,” and says mitigation measures may have affected 2021–22. The 2024–25 figures are preliminary. CDC does not count flu illnesses directly: it estimates them from hospitalizations, using a ratio of illnesses to hospitalizations for each age group that was estimated during the 2009 pandemic, so every rate per 10,000 people with symptoms depends on those ratios.

  15. 15. ≪1 have a serious side effect, 0 die

    Anaphylaxis, 1.35 per million doses (McNeil 2016), plus Guillain-Barré syndrome, CDC’s “one to two additional GBS cases per million doses,” plus shoulder injury, 7.8 per million (Hesse 2020): about 10 to 11 per million, or about 0.1 per 10,000.

    One other event is not shown. Febrile seizures: CDC reports a small excess in children aged 6 to 23 months when the flu shot is given the same day as PCV13 or DTaP, “at most 30 febrile seizures in 100,000 children vaccinated” with that combination, or 3 per 10,000 of those children. The excess is specific to that age group and that combination of shots; most people who get the flu shot are adults, for whom it does not arise, and no source gives a rate across all doses.

    All rates are for the injectable inactivated and recombinant vaccines, not the nasal spray, and are per dose; CDC says some children aged 6 months to 8 years need two doses per season.

  16. 16. ≪1 severe allergic reaction

    McNeil 2016: 10 confirmed cases of anaphylaxis after 7,434,628 doses of inactivated trivalent flu vaccine given alone, 1.35 per million (95% CI 0.65–2.47), or 0.0135 per 10,000.

  17. 17. ≪1 Guillain-Barré syndrome; flu raises this risk more than the shot does

    CDC: in seasons where a link is found, it is “one to two additional GBS cases per million doses of flu vaccine.” Kwong 2013 counted GBS admissions above the background rate in the weeks after each exposure: about 1 extra per million flu vaccinations, compared with about 17 extra per million medical visits for flu (visits coded as influenza, not laboratory-confirmed infections).

  18. 18. ≪1 shoulder injury

    Hesse 2020 followed 2,943,493 people vaccinated against flu in the Vaccine Safety Datalink and compared shoulder bursitis with onset in the two days after injection against the background rate a month later: 7.78 excess cases per million vaccinated (95% CI 2.19–13.38), or 0.078 per 10,000. Subdeltoid bursitis is inflammation of the shoulder, with pain and limited motion. The authors propose a needle placed too high, into or near the bursa, as the mechanism, but “cannot conclude from our data that improper technique was a factor.”

  19. 19. 0 die (of 10,000 who get the flu shot)

    Death is not impossible, but it is vanishingly unlikely.

    McNeil 2016 reviewed 33 confirmed cases of anaphylaxis after vaccination, 10 of them after the flu shot: “There were no deaths, and only 1 (3%) patient was hospitalized.” The Pink Book reviewed adverse-event reports on the recombinant flu vaccine from 2013 to 2016: “There were four serious reports but no death was reported.”

    Miller 2015 reviewed deaths reported after vaccination and found that “the vast majority of reported deaths were coincidental.” The exceptions that apply to the flu shot are anaphylaxis, which “is serious and can be fatal,” and Guillain-Barré syndrome. The 1976 swine-flu vaccine caused GBS with 53 deaths; the seasonal vaccines since have not. Miller: “Approximately 5% of Guillain-Barré syndrome cases are fatal,” but the risk of death from vaccine-associated GBS “would have to be considered theoretical.” Even if it were real, 1 to 2 excess GBS cases per million doses, times 5%, is one death per 10 to 20 million doses.

  20. 20. A minor sore arm, aches, or fatigue for a few days is common.

    CDC: side effects of the flu shot “disappear on their own in a few days.” In adults, the Fluarix insert reports pain at the injection site 55%, muscle aches 23%, fatigue 20%, headache 19%; the Fluzone insert reports pain 53.7%, muscle aches 30.8%, headache 30.3%, malaise 22.2%, fever 2.6%.

  21. 21. ≪1 means much less than one: a few per million each.

    Anaphylaxis at 1.35 per million doses, plus CDC’s “one to two additional GBS cases per million doses,” plus shoulder injury at 7.8 per million, is about 10 to 11 per million.

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An information sheet from Calypta Health · © 2026 Calypta Systems

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