Influenza cases are rising

After unusually low influenza activity in 2020 and 2021, cases have been rising in the 2022-23 season.

Not everyone who contracts the flu visits a doctor, and not all flu deaths occur in the hospital, so the Centers for Disease Control and Prevention use mathematical modeling based on their surveillance data to estimate the total number of illnesses and deaths. The model considers factors such as testing frequency, the likelihood of seeking medical care and under-reporting on death certificates.

Influenza 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, counting deaths “only 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 the 2019-20 season. This contrasts with the CDC estimate of 25,000 flu deaths over the same season.

Still, 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. In comparison, 932 deaths from influenza were recorded in the 2020-21 season.

Aspects of the coronavirus pandemic have led to lower flu activity, health officials explained. Fewer people got routine health checks or tested for influenza in 2020 and 2021 than in previous years. Also, health measures to slow the transmission of COVID-19, such as quarantines, school closures and face masks, helped reduce the spread.

The CDC provides mortality data at the state level, but data releases are delayed. The most current data available is from 2020, according to USA Facts. USA Facts is a nonprofit organization founded by Steve Ballmer, an American agnate and investor who served as chief executive officer of Microsoft from 2000 to 2014.

That year, the states with the highest age-adjusted flu death rates were in Kansas, West Virginia and North Dakota, while Utah had the fewest, USA Facts reported.

Most flu deaths occur among Americans aged 65 or older. For the 2021-22 season, Americans 65 and older died from influenza at a rate of 6.9 per 100,000. That mortality rate was more than three times higher than for any other age group.

Vaccinations prevented an estimated 6,300 deaths in the 2019-20 flu season.

In the past decade, vaccinations have prevented as few as 3,500 deaths in the 2018-19 season, and as many as 12,000 deaths in the 2013-14 season. Mandatory reporting has shown that 80% of children who die from the flu are unvaccinated, USA Facts related.