BNT162b2 vaccine induces moderate immunity against SARS-CoV-2 in children 5-11 years old

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In a recent study published in the New England Journal of Medicineresearchers evaluated the efficacy of the BNT162b2 vaccine against the concerning new variant (VOC) Omicron of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in children 5 to 11 years of age.

Only a few studies have assessed the effectiveness of the messenger ribonucleic acid (mRNA) vaccine BNT162b2 against SARS-CoV-2 in real-world settings. In addition, there is little evidence of its effectiveness in preventing Omicron infections in children 5 to 11 years old.

Study: Efficacy of BNT162b2 vaccine against Omicron in children 5-11 years old. Image Credit: Ira Lichi/Shutterstock

About the study

In the current study, researchers identified a cohort of five- to 11-year-old children vaccinated against coronavirus disease 2019 (COVID-19) on or after November 23, 2021, with BNT162b2 in Israel. They compared whether vaccination prevented them from being infected with Omicron against matched unvaccinated controls. They documented vaccine (VE) efficacy against asymptomatic and symptomatic cases 14–27 days after the first and seven–21 days after the second dose(s) of BNT1262b.

The team estimated the cumulative incidence (risk) of each outcome in the test and control groups using the Kaplan-Meier estimator through January 7, 2022. Additionally, they calculated the VE for different age subgroups (five or six years old, seven to nine years old, and 10 or 11 years old). They defined VE as a minus the hazard ratio. Notably, they also estimated the proportion of Omicron cases daily. They used patient samples sequenced by the Israeli Ministry of Health after testing positive for COVID-19 by reverse transcription-polymerase chain reaction (RT-PCR).

Study results

Although 136,127 children covered by Clalit Health Services (CHS) were eligible for the study, the final study population included 94,728 vaccinated children and an equal number of unvaccinated controls. Additionally, the CHS required that all of these children have at least 12 months of CHS membership, no prior positive RT-PCR tests, valid residency in Israel, and no interaction with healthcare personnel or hospital within three years. days before registration. in the study.

Both study groups had similar COVID-19 testing rates and risk factors for severe COVID-19. Similarly, the test and control groups had a similar incidence of SARS-CoV-2 infections and symptomatic COVID-19 at the start of follow-up. However, slight discrepancies became noticeable for both study results after day 28.

The median age of the study population was eight years, with 49% women and 17% obese children. The average follow-up time after the first vaccine dose was 17 days. At 14 to 27 days after the first vaccine dose, the authors noted a 17% and 18% VE against SARS-CoV-2 infection and symptomatic COVID-19, respectively. For seven to 21 days after the second vaccine dose, VE against SARS-CoV-2 infection and symptomatic COVID-19 was 51% and 48%, respectively.

Omicron was responsible for approximately two-thirds of new infections in children who had received a two-dose regimen of BNT1262b as of December 21, 2021. As of December 31, 2021, more than 85% of identified cases were due to breakthrough infections of Omicron. Subgroup analyzes showed that VE against SARS-CoV-2 infection was 68% in children five to six years old. In the age group of seven to nine years, the LE was 56%, and in children aged 10 or 11, the LE was 38%.

conclusion

Walter et al. showed that the estimated EV of BNT1262b against symptomatic COVID-19 was higher against SARS-CoV-2 Delta VOC, close to 91%. In the present study, the VE of BNT1262b against symptomatic COVID-19 versus Omicron was just 48%. However, Walter et al. documented only one event in both study groups by day 28 post-vaccination, while the authors documented two events. Another recent study estimated the VE against Omicron between 30% and 68% for adults and adolescents. However, these VE estimates might not apply to young children because their vaccine dosage and immunity differ from that of adolescents and adults.

The Pediatric Research Observing Trends and Exposures in COVID-19 Timelines (PROTECT) study estimated a 31% VE against Omicron among 1,052 children aged five to 11 years. However, in the present study, the authors observed minimal differences in VE or risk between vaccinated and unvaccinated children after the first vaccine dose. The majority of the differences between the two study groups only became apparent after the second dose of vaccine.

Overall, vaccination with BNT162b2 conferred moderate protection in children 5-11 years of age. The protection conferred by BNT1262b was not uniform in all age groups; however, BNT1262b showed the greatest efficacy against SARS-CoV-2 infection and symptomatic COVID-19 in the youngest age group of five- or six-year-old children. Future studies should assess long-term VE in children to help develop age-appropriate vaccination strategies and further investigate the potential dose effect in different age groups of children and other subpopulations.

Journal reference:

  • Efficacy of BNT162b2 vaccine against Omicron in children 5-11 years old, Chandra J. Cohen-Stavi, Ori Magen, Noam Barda, MD, Shlomit Yaron, Alon Peretz, Doron Netzer, Carlo Giaquinto, Ali Judd, Leonard Leibovici, Miguel A Hernán, Marc Lipsitch, Ben Y. Reis, NEJM 2022, DOI: 10.1056/NEJMoa2205011, https://www.nejm.org/doi/full/10.1056/NEJMoa2205011
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