#15,483
The 2019-2020 flu season - which was abruptly interrupted and largely suppressed by the arrival of COVID-19 last March - officially came to an end last week (see FluView chart above). A moderate flu season, it featured two consecutive waves - initially of Influenza B, then overtaken by H1N1 - both of which tend to affect younger cohorts.
On January 10th, 2020 the CDC issued a HAN Advisory and a FluView report warning of elevated flu activity, and its impact on children.Elevated Influenza Activity: Influenza B/Victoria and A(H1N1)pdm09 Viruses are the Predominant Viruses
The Centers for Disease Control and Prevention reminds clinicians that influenza B viruses can cause severe illness in people of all ages, including children. CDC continues to recommend influenza vaccination and prompt antiviral treatment of high-risk outpatients and hospitalized patients with suspected influenza.
Only a decade ago, Influenza B was viewed generally as a `less serious' infection than influenza A - affecting mainly children - and producing relatively mild illness in adults. A study, published in 2014 in the Clinical Infectious Diseases Journal, challenged the old ideas about influenza B.
Comparing Clinical Characteristics Between Hospitalized Adults With Laboratory-Confirmed Influenza A and B Virus Infection
Su Su Sandra S. Chaves Alejandro Perez Tiffany D'Mello Pam D. Kirley Kimberly Yousey-Hindes Monica M. Farley Meghan Harris Ruta Sharangpani Ruth Lynfield ...
Clinical Infectious Diseases, Volume 59, Issue 2, 15 July 2014, Pages 252–255,
https://doi.org/10.1093/cid/ciu269 Published: 18 April 2014
ABSTRACT
We challenge the notion that influenza B is milder than influenza A by finding similar clinical characteristics between hospitalized adult influenza-cases. Among patients treated with oseltamivir, length of stay and mortality did not differ by type of virus infection.
The CDC, which partnered in this study, published the following summary:
New CDC Study Compares Severity of Illness Caused by Flu A and B Viruses
Influenza B virus infections can be just as severe as influenza A virus infections
(SNIP)
This contradicts a common misconception that flu B viruses are associated with milder disease than flu A viruses.
This past flu season - while moderate overall - produced a record number (n=189) of pediatric flu-related deaths (outside of a pandemic), and hospitalization rates in small children (0-4 years old) and younger adults (18-49 years old) were higher than observed during the 2009 H1N1 pandemic.
Of particular note, nearly 2/3rds of this year's pediatric flu deaths were attributed to influenza B.
Had the height of 2019-2020 flu season not been quashed by the arrival of COVID-19, these numbers would likely have been higher. Although pediatric flu deaths have been a `reportable' disease by the CDC since 2004, it is estimated that only between 1/3rd and 1/4th of all pediatric flu deaths are captured by surveillance.
Which means the true toll this year is probably closer to 600 pediatric deaths.
On Friday the CDC published two wrap-up reports on this past flu season, links and excerpts you'll find below.
Estimated Influenza Illnesses, Medical visits, Hospitalizations, and Deaths in the United States — 2019–2020 Influenza Season
(EXCERPTS)
2019–2020 Burden Estimates
Influenza activity in the United States during the 2019–2020 season began to increase in November and was consistently high through January and February. The season was characterized by two consecutive waves of activity, beginning with influenza B viruses and followed by A(H1N1)pdm09 viruses. Overall, influenza A(H1N1)pdm09 viruses were the most commonly reported influenza viruses this season. Activity began to decline in March, perhaps associated with community prevention measures for COVID-19 (5-6). The 2019-20 season is described as having moderate severity; however, the effect of influenza differed by age group and the severity of the season in some age groups was higher. Hospitalization rates among children 0-4 years old and adults 18-49 years old were higher than observed during the 2009 H1N1 pandemic (6).
CDC estimates that the burden of illness during the 2019–2020 season was moderate with an estimated 38 million people sick with flu, 18 million visits to a health care provider for flu, 400,000 hospitalizations for flu, and 22,000 flu deaths (Table 1). The number of cases of influenza-associated illness, medically attended illnesses, hospitalizations, and deaths were lower than some more recent seasons and similar to other seasons where influenza A(H1N1)pdm09 viruses dominated (7, 8).
The 2019–2020 influenza season was atypical in that it was severe for children aged 0-4 years and adults 18-49 years where rates of infections, medically attended illnesses, hospitalizations, and deaths were higher than those observed during the 2017-2018 season, a recent season with high severity (7). The burden of influenza and the rates of influenza-associated hospitalization are usually higher for the very young and the very old, and while this was observed during the 2019–2020 season, rates of hospitalization in adults aged 18-49 years were the highest seasonal rates seen since the 2017-2018 season (Table 2). These rates mean that an estimated 15 million cases of influenza in younger adults (aged 18-49 years), which is the highest number of infections for this age group since CDC began reporting influenza burden estimates in the 2010-11 season.
CDC’s estimates of hospitalizations and mortality associated with the 2019–2020 influenza season show the effects that influenza virus infections can have on society. More than 52,000 hospitalizations occurred in children aged < 18 years and 86,000 hospitalizations among adults aged 18-49 years. Forty-three percent of hospitalizations occurred in older adults aged ≥65 years. Older adults also accounted for 62% of deaths, which is lower than recent previous seasons. These findings continue to highlight that older adults are particularly vulnerable to severe disease with influenza virus infection. An estimated 7,800 deaths (36% of all deaths) occurred among working age adults (aged 18–64 years), an age group for which influenza vaccine coverage is often low (9). This also underscores that influenza viruses can affect individuals of any age and prevention measures such as vaccination are important to reducing the impact of the seasonal epidemics on the population and healthcare system.
Deaths in children with laboratory-confirmed influenza virus infection have been a reportable disease in the United States since 2004; 188 deaths were reported for the 2019-20 season as of September 19, 2020. However, influenza-associated pediatric deaths are likely under-reported, as not all children whose death was related to an influenza virus infection may have been tested for flu (10,11). Therefore, we used a mathematical model to estimate the total number of pediatric deaths based on hospitalization rates and the frequency of death in and out of the hospital using death certificates. We estimate that at least 434 deaths associated with influenza occurred during the 2019-2020 season among children aged <18 years.
Pediatric Flu Deaths Reach New High Mark During 2019-2020
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October 2, 2020 – CDC today reported 1 new seasonal flu-related death in a child that occurred during week 4 of the 2019-2020 season, bringing the total number of flu deaths in kids reported to CDC for last season to 189. This surpasses the highest recorded number for pediatric flu deaths reported during a regular flu season, which occurred during the 2017-2018 flu season when 188 pediatric flu deaths were reported to CDC.
Among the 189 reported pediatric flu deaths:
- 42% (80) occurred in children younger than 5 years old
- 11 occurred in children younger than 6 months and thus too young to get a flu vaccine
- 58% (109) deaths occurred in children 5-17 years old
- Of the 176 pediatric deaths among children with known information on medical conditions, 77 (44%) had a pre-existing medical condition.
- Nearly two-thirds of the deaths were attributed to influenza B infections.
This tragic milestone underscores how serious flu can be and serves as a reminder of the importance of an annual flu vaccine. In 2019-2020, only 21 percent of children eligible for vaccination were fully vaccinated against flu. This percentage was similar to past seasons.
While we don't know if influenza activity will continue to be suppressed this winter by COVID-19, or how well this year's vaccine will match circulating flu strains, we have seen evidence that co-infeciton with influenza and SARS-CoV-2 can produce much worse outcomes (see PHE Study: Co-Infection With COVID-19 & Seasonal Influenza).
Even without the addition of COVID-19, influenza is a proven killer of adults and children.
Which is why I've already gotten my flu (and pneumonia) vaccine this year, and hope you'll consider doing so yourself.
