During the 2022–2023 US flu season, an estimated 31.91 million people experienced symptoms of the influenza virus.
After two years of unusually low levels of recorded flu activity, cases jumped from 2022 to 2023, according to preliminary Centers for Disease Control and Prevention (CDC) estimates.
When is the flu season?
The CDC determines the start and end of flu season by monitoring flu activity — illnesses, medical visits, and hospitalizations — through its influenza surveillance systems. Most seasons begin in October, peak between December and February, and continue through May.
The 2022–23 flu season began in October 2022 and continued until early September 2023, according to the CDC. Nearly 85% of cases during this season were recorded between October and January based on data from the National Center for Health Statistics.
For context, flu activity during the 2021-2022 season began to increase in November and remained elevated until mid-June.
Why were flu cases so low during the pandemic?
The CDC attributed low flu activity during the pandemic to COVID-19 mitigation efforts that are also effective in slowing the spread of the flu, such as the use of face masks, staying home, reduced travel, school closures, and more. As a result, estimates of those impacted by the 2021–22 flu season are as much as 90% lower than in past years.
The CDC described flu activity in the 2020–21 flu season as “unusually low.” It was the lowest flu activity since the CDC first began collecting data in 1997.
Flu cases rebounded during the 2021–22 season compared to the previous year, but were the second lowest in over a decade.
How many people die from the flu?
The CDC estimates that between 12,000 and 52,000 people died of the flu annually between 2010 and 2020. The 2017–18 flu season had more related deaths than any other season: an estimated 52,000.
According to CDC data, the flu led to 15 million medical visits, over 360,000 hospitalizations, and 21,410 deaths during the 2022–23 season.
Since not everyone sick with the flu visits a doctor, and not all flu deaths occur in the hospital, the CDC uses mathematical modeling based on its surveillance data to estimate the total number of illnesses and deaths. This model considers factors like testing frequency, the likelihood of seeking medical care, and underreporting on death certificates.
The flu can lead to death by pneumonia, congestive heart failure, or chronic obstructive pulmonary disease — in which case flu testing may occur too late or not at all. The CDC says, “Only counting deaths where influenza was recorded on a death certificate would be a gross underestimation of influenza’s true impact.”
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As an example, data from the National Center for Health Statistics Mortality Surveillance System, which is based on death certificate records, shows 9,435 people died from the flu in 2019–20 season. This contrasts with the CDC estimate of 25,000 flu deaths over the same season.
Still, the unadjusted death certificate data can allow for an imperfect comparison of flu’s impact from year to year.
During the 2017–18 flu season, the mortality surveillance system recorded 15,620 deaths via death certificates, the most deaths in the last five years. By comparison, it recorded 9,843 deaths in the 2022–23 season.
Which state has the most flu deaths?
The CDC also provides mortality data at the state level, but nationwide data releases are delayed. The latest data from CDC Wonder is from 2020.[1]
Kansas, West Virginia, and North Dakota had 2020’s highest age-adjusted death rates.
How does flu risk vary by age?
For the 2022–23 season, 26.6 per 100,000 Americans 65 and older died from the flu. That mortality rate was more than three times higher than any other age group.
In total, an estimated 15,399 Americans 65 and older died from the flu during the 2022-23 season, nearly 72% of all flu-related deaths.
How effective are vaccinations against the flu?
Vaccinations prevented an estimated 22,446 hospitalizations and 897 deaths in the 2021–2022 flu season. In the past decade, they have prevented as few as 2,840 deaths in 2018–2019 and as many as 12,166 deaths in 2013–2014. According to mandatory reporting between 2010 and 2020, 80% of children who died from the flu were unvaccinated.
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[1] Influenza data reporting differs across states and local jurisdictions.
