The average flu season kills thousands of Americans each year, according to data from the Centers for Disease Control and Prevention (CDC). After unusually low recorded flu activity between 2020 and 2021, cases of the disease have jumped back up in 2022.
According to the CDC, the drop in flu cases during the pandemic can be attributed to a decline in routine health checks, meaning fewer people were tested for influenza than in previous years, and the wide range of health measures taken in response to COVID-19.
As a result, preliminary estimates of those impacted by the 2021-22 flu season are as much as 90% lower than in past years.
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 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.
The 2021-22 flu season began in October 2021 and continued until mid-June 2022, with a spike in cases in late November and a second spike in early March.
Flu cases rebounded during the 2021-22 season compared to the previous year, but were the second lowest in over a decade.
The CDC attributed low flu activity in both the 2020-21 and 2021-22 flu seasons 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, the last two flu seasons have deviated from historical trends.
The CDC estimates that an average of 35,000 people died of the flu each year over the past decade. More people died during the 2017-18 flu season than any other season in the last decade, with an estimated 52,000 flu-related deaths.
According to preliminary estimates from the CDC, there were approximately nine million flu-related illnesses, four million flu-related medical visits, 100,000 flu-related hospitalizations, and 5,000 flu deaths during the 2021-22 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. According to the CDC, “Only counting deaths where influenza was recorded on a death certificate would be a gross underestimation of influenza’s true impact.”
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, 15,620 deaths were recorded via death certificates in the mortality surveillance system, the largest number of flu deaths in the last five years. By comparison, 931 flu deaths were recorded in the 2020-21 season.
The CDC also provides mortality data at the state level, but data releases are delayed. 2020 is the most current data available. .
In 2020, the states with the highest age-adjusted death rates were Kansas, West Virginia, and North Dakota.
Most flu deaths occur among Americans aged 65 or older. For the 2021-22 season, the most current data available, 6.9 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.
Vaccinations prevented an estimated 6,300 deaths in the 2019-2020 flu season. In the past decade, they have prevented as few as 3,500 deaths in the 2018-2019 season and as many as 12,000 deaths in the 2013-2014 season. According to mandatory reporting, 80% of children who die from the flu are unvaccinated.
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