CDC: Last Year’s Flu Shot Was Less Than 50% Effective for Children and Adolescents

During the 2022–2023 flu season, the influenza vaccine was less than 50 percent effective at preventing emergency department/urgent care visits and hospitalizations among children and adolescents, according to a study funded by the Centers for Disease Control and Prevention (CDC).

The analysis, published Nov. 16, 2023, in Clinical Infectious Diseases, found the seasonal influenza vaccine was only 48 percent effective overall at reducing the risk of influenza-A-associated emergency department (ED) or urgent care (UC) visits, and only 40 percent effective at preventing hospitalizations.

Researchers analyzed acute respiratory illness-associated ED and UC visits or hospitalizations at 55 hospitals and 107 ED or UC sites within the VISION vaccine effectiveness network—a multistate collaboration with the CDC. Children and adolescents 6 months to 17 years were tested for influenza between October 2022 and March 2023.

Researchers estimated influenza A vaccine effectiveness using a test-negative design—a popular method for determining vaccine efficacy that uses the same clinical case definition for both cases and controls and distinguishes which patients are in each group with subsequent laboratory testing. In other words, the effectiveness of the influenza vaccine was estimated by comparing influenza vaccination status in patients testing positive for influenza with those testing negative for influenza.

According to the study, 13,547 of 44,787 qualified ED/UC visits and 263 of 1,862 hospitalizations were positive for influenza A. Among ED/UC patients, 15.2 percent of influenza-positive cases and 27.1 percent of influenza-negative cases were vaccinated.

The vaccine was 44 to 52 percent effective—or 48 percent effective “overall,” 47 to 58 percent effective among children aged 6 months to 4 years, and 30 to 45 percent effective among those aged 9 to 17 years old.

Among hospitalizations, 17.5 percent of influenza-positive cases were vaccinated compared with 33.4 percent of influenza-negative patients. Vaccine efficacy was 6 to 61 percent—or 40 percent “overall,” 23 to 75 percent among children ages 6 months to 4 years, and 2 to 70 percent among those 5 to 17 years old. Despite vaccine efficacy numbers, researchers said the influenza vaccine is a “critical tool to prevent moderate-to-severe influenza illness in children and adolescents.”

Findings Identify Associations, Not Causal or Inferred Effectiveness

Linda Wastila, professor and Parke-Davis chair of geriatric pharmacotherapy with a doctorate in health policy, told The Epoch Times in an email that she found the study a bit confusing and the authors’ claims of effectiveness against preventing emergency room and hospital admissions a “bit of a stretch.”

“The authors look at subjects who enter the hospital, although the primary (and secondary) reasons for admission are not provided or controlled for, with subjects possibly [admitted] for other conditions (e.g., pneumonia, RSV, broken limbs) and, in testing, found to be positive WITH influenza rather than admitted FOR influenza. The authors didn’t control for many factors using multivariable approaches, so there is no control in their VE [vaccine efficacy] calculations for variability by site or in the subjects themselves,” Ms. Wastila said.

“Although the authors present tabular findings (Table 2) on subjects’ health status, these are essentially descriptive or, at best, cross-tabular, NOT causal, associations between vaccine status and influenza negativity,” she added.

Ms. Wastila said another serious shortcoming the authors noted themselves is the considerable variation across and within the three healthcare systems used for enrollment.

“I dislike using the term ‘cherry pick,’ but without randomization and/or matching of cases with controls, we cannot rule out explicit and/or implicit biases made at the site, principal investigator, and provider levels in identifying subjects,” she said. “In sum, based on the lack of matched cases/controls and lack of statistical control for covariates and confounders, at best, this study’s findings reflect descriptive findings demonstrating associations, not causal or inferred effectiveness.”

CDC Redefines Vaccine Efficacy for Influenza Vaccine

The agency conducts yearly studies during flu season to help determine how well the vaccine works. Vaccine effectiveness studies help assess the “value of flu vaccination as a public health intervention.” Although the test-negative design is a common method of determining vaccine efficacy, a 2021 Department of Health and Human Services study said “particular care” must be taken when using this method to determine whether a vaccination reduces disease severity in breakthrough infections.

The CDC rolled out a digital ad campaign in September to rebrand the influenza vaccine and redefine expectations about what a yearly flu shot could and couldn’t do amid breakthrough cases. The agency’s new messaging is that the flu shot wouldn’t prevent a person from getting sick but would prevent severe illness should one still get sick.

This is similar to the shift in messaging adopted by U.S. regulatory agencies with COVID-19 vaccines when breakthrough COVID-19 cases started piling up among the vaccinated. U.S. health officials then admitted the shots did not prevent COVID-19 or transmission of the virus to others, and vaccine efficacy was redefined by whether the vaccine prevented hospitalizations and death.

According to CDC data, the influenza vaccine was 54 percent effective during the 2022–2023 influenza season and 36 percent effective during the 2021–2022 season. During the previous ten years, vaccine efficacy for the influenza vaccine has ranged from 19 to 52 percent effective.

This study was conducted by the CDC—which is currently marketing and promoting influenza vaccination—and its researchers and affiliates. The Epoch Times contacted the CDC for comment but has not received a response.

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