'High Severity' Flu Season Among Children Spotlights Importance of Vaccination

The Centers for Disease Control and Prevention (CDC) has classified the 2022-2023 influenza season as “high severity” for individuals younger than 18 years of age.

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In the CDC’s Morbidity and Mortality Weekly Report, the agency noted that this flu season began earlier than most prior seasons, in October, and showed a return to levels that preceded the COVID-19 pandemic. Along with increased pediatric influenza hospitalization rates, the “triple-demic” with the flu, COVID-19, and respiratory syncytial virus caused a strain on healthcare systems, according to the CDC.

“Nationally, the incidences of influenza-associated outpatient visits and hospitalization for the 2022–23 season were similar for children aged <5 years and higher for children and adolescents aged 5–17 years compared with previous seasons,” the CDC wrote. “Peak influenza-associated outpatient and hospitalization activity occurred in late November and early December.”

The CDC classifies the severity of flu season based on the percentage of all outpatient visits with influenza-like illness, rates of laboratory-confirmed influenza hospitalization, and the percentage of all deaths because of influenza, which is defined as fever plus cough or sore throat.

The CDC stated that a lower proportion children and adolescents hospitalized for the flu during the 2022–23 season were vaccinated (18.3%) compared with previous seasons (35.8%–41.8%).

“Early influenza circulation, before many children and adolescents had been vaccinated, might have contributed to the high hospitalization rates during the 2022–23 season,” the agency stated.

Administration of antiviral treatments occurred in 64.9% of hospitalized patients compared with rates of 80.8% to 87.1% pre–COVID-19 pandemic.

In children younger than 5 years of age, estimated flu-associated medical visits, hospitalization, and mortality were higher than among the 5 to 17 years of age group, whose rates were higher in 2022-2023 than any other season since 2016-2017.

Individuals younger than 5 years of age had the second highest rates of flu-associated medical visits and hospitalizations from 2022-2023 than any year since 2016-2017, with 11,443 medical visits per 100,000 and 119 hospitalizations per 100,000.

The report noted 2762 flu-associated hospitalizations among individuals younger than 18 years of age from October 1, 2022, to April 30, 2023, among whom 57.4% were male, with a median age 5 years.

Among this cohort, 50.5% had an underlying condition, which was found to be similar to recent flu seasons, with the most common being asthma, neurologic disorders, and obesity. The CDC found that 57.1% of the total pediatric hospitalizations were reported during October and November 2022.

An estimated 18.3% of those hospitalized were vaccinated for the flu, which fell from 35.8%-41.8% in 2016-2017 through 2021-2022. The current flu season was estimated to be the fourth highest severity season among children and adolescents since 2009 during the influenza A(H1N1) pandemic, according to the CDC.

“The 2022–23 influenza season was classified as high severity for children and adolescents based on influenza-associated outpatient visits, hospitalization rates, and deaths,” the agency wrote. “Among hospitalized children and adolescents with influenza, receipt of influenza vaccine was lower than that during previous seasons, which might have been in part related to most influenza hospitalizations occurring earlier. The proportion of pediatric hospitalizations treated with influenza antiviral medication was lower than in pre–COVID-19 pandemic seasons; prompt antiviral treatment is important for symptomatic patients hospitalized with influenza. All persons aged ≥6 months are recommended by CDC to receive the annual seasonal influenza vaccine, ideally by the end of October.”

Reference

High influenza incidence and disease severity among children and adolescents <18 years – United States, 2022-23 season. Morbidity and Mortality Weekly Report. October 13, 2023. Accessed November 28, 2023. https://www.cdc.gov/mmwr/volumes/72/wr/mm7241a2.htm