Determining the Efficacy of Bivalent COVID-19 Vaccines in Children and Adolescents

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Generally speaking, hospitalizations and death among children and adolescents associated with SARS-CoV-2—the virus that causes COVID-19—are lower among than for adults, but that does not mean that precautions shouldn’t be taken. Data have shown that as of Dec. 31, 2023, there were 911 COVID-related deaths for US children and adolescents.

The Omicron variant is often more transmissible and has the ability to elude vaccine-induced immunity, so as a result, the FDA approved the use of a bivalent mRNA COVID-19 vaccine containing both ancestral and Omicron BA.4/5 strains. On Sept. 1, 2022, it was recommended for individuals 12 years of age and older, and on Oct. 12 of that same year, it was approved for children ages 5-11.

Even after these approvals, there still lies mystery and skepticism as to these jabs’ effectiveness in younger patients. In an effort to provide additional clarity, a cohort study published in JAMA Network¹ was designed to determine their efficacy.

From Sept. 4, 2022-Jan. 31, 2023, the investigators began the process by analyzing sites around the United States. They merged data from three prospective cohort studies (Pediatric Research Observing Trends and Exposures in COVID-19 Timelines [PROTECT], CASCADIA, and Community Vaccine Effectiveness [CoVE], which is an expansion of the Household Influenza Vaccine Evaluation [HIVE] cohort). After obtaining informed consent from parents or guardians, 2,959 children and adolescents living in Arizona, Michigan, Oregon, Texas, Utah, and Washington (even those who lived in the same house), were included.

These parents or guardians completed an enrollment survey on any chronic medical conditions, demographics (race and ethnicity), COVID vaccination history, and prior SARS-CoV-2 infection. Blood samples were also collected, and individuals had to self-collect upper respiratory specimens every week.

Of the 2959 participants (47.8% were female, with a median age 10.6 years [IQR, 8.0-13.2 years]; 64.6% were non-Hispanic White) included in this analysis, 25.4% were administered a bivalent COVID-19 vaccine dose.

During the study period, the study revealed that 426 participants (14.4%) had a laboratory-confirmed SARS-CoV-2 infection. Out of that sample size,

• 184 (43.2%) had symptomatic COVID-19
• 383 (89.9%) were either not vaccinated or had received only monovalent COVID-19 vaccine doses (1.38 SARS-CoV-2 infections per 1000 person-days)
• 43 (10.1%) had been administered a bivalent COVID-19 vaccine dose (0.84 SARS-CoV-2 infections per 1000 person-days).

The bivalent vaccine’s efficacy against SARS-CoV-2 infection was 54.0% (95% CI, 36.6%-69.1%), while vaccine effectiveness against symptomatic COVID-19 was 49.4% (95% CI, 22.2%-70.7%). Following vaccination, the median observation time was 276 days (IQR, 142-350 days) for participants who received only monovalent COVID-19 vaccine doses, compared to 50 days (IQR, 27-74 days) for participants who received a bivalent COVID-19 vaccine dose.

This cohort study also did present its share of limitations, including that RT-PCR testing methods and the list of COVID-19 symptoms surveyed varied by cohort, which could change how one defines a SARS-CoV-2 infection or symptoms; weekly/symptomatic RT-PCR testing that occurred before the start of the study was only accessible among one subset of participants; there was recall bias when reporting prior SARS-CoV-2 infection; there was a failure to consider immunocompromised status and the social vulnerability index; and the investigators were working with limited sample sizes.

Despite these limitations, the authors concluded that “the bivalent COVID-19 vaccine protected children and adolescents against SARS-CoV-2 infection and symptomatic COVID-19. These data demonstrate the benefit of COVID-19 vaccine in children and adolescents. All eligible children and adolescents should remain up to date with recommended COVID-19 vaccinations.”

Reference

1. Feldstein LR, Britton A, Grant L, et al. Effectiveness of Bivalent mRNA COVID-19 Vaccines in Preventing SARS-CoV-2 Infection in Children and Adolescents Aged 5 to 17 Years. JAMA. 2024;331(5):408–416. doi:10.1001/jama.2023.27022