Study reports substantial loss of protection one month after full vaccination against SARS-CoV-2 BNT162b2 in children

A recent study published on the medRxiv* The preprint server evaluated the efficacy of Pfizer’s BNT162b2 vaccine in children aged 17 years or younger following the emergence of the Omicron variant of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2).

Study: Efficacy of the BNT162b2 vaccine in children 5-11 and 12-17 years old in New York after the emergence of the Omicron variant. Image Credit: Melinda Nagy/Shutterstock

Coronavirus disease 2019 (COVID-19) infections have been diagnosed in more than 0.8 million people age 17 or younger in New York State (NYS), United States (US) . Although observational studies and randomized trials, conducted during the SARS-CoV-2 delta or previous waves, observed that the BNT162b2 vaccine is effective against COVID-19 infection in people aged 5 to 17 years . Children aged 5 to 11 receive a 10 mcg dose of vaccine compared to 30 mcg for 12 to 17 year olds. However, actual vaccine efficacy (VE) remains poor for the older cohort, especially since the emergence of the Omicron variant.

The study

In the present study, researchers are evaluating VE in BNT162b2 vaccinees aged ≤ 17 years during the Omicron wave of COVID-19 infections. Three linked databases to analyze COVID-19 outcomes in NYS children were used – Citywide Immunization Registry (CIR), NYS Immunization Information System (NYSIIS) and the Electronic Clinical Laboratory Reporting System (ECLRS). The CIR and NYSISS track immunization data for New York City (NYC) and NYS, respectively, while the ECLRS contains COVID-19 test reports. The Electronic Health Response Data System (HERDS) stores inpatient data and new COVID-19 admissions.

COVID-19 outcomes were compared between fully vaccinated and unvaccinated children. The authors assessed two outcomes: a) COVID-19 cases reported to the ECLRS with a positive nucleic acid or antigen test and b) new COVID-19 admissions based on HERDS entries. SARS-CoV-2 cases and hospital admissions were counted weekly for vaccinated and unvaccinated children between November 29, 2021 and January 30, 2022. Incidence rate ratios (IRRs), measured as the ratio of unvaccinated to vaccinated rate, were determined and VE was calculated as 1-(1/IRR). Additionally, time since vaccination was examined for fully vaccinated children between December 13, 2021 and January 2, 2022.


In the NYS, 365,502 (23.4%) of children ages 5-11 and 852,384 (62.4%) of children ages 12-17 were fully vaccinated as of January 30, 2022. The TRI for cases of COVID-19 decreased from 6.7% with a VE of 85% at the start of the study to 2.9% (VE=66%) by December 13, 2021 and 2% (VE=51%) by January 24 for children aged 12 to 17.

For ages 5-11, the IRR fell to 1.1% (VE=12%) as of January 24. Protection against hospitalization was greater than against COVID-19 infections. The IRR for hospitalization was 1.9 with a VE of 48% for 5-11 year olds as of January 24, 2022, compared to 3.7 (VE = 73%) for the 12-17 year old group. During the week of January 24, 2022, the VE against COVID-19 infection for an 11-year-old child was 11% lower than 67% for a 12-year-old child.

For time since vaccination from 12 to 17 years, the IRR was 4.3 with a VE of 76% in ≤ 13 days since full vaccination, which dropped to 2.3 (VE = 56%) 4 to 5 weeks after full immunization. Similarly, the IRR was 2.9 (VE = 65%) for the age group 5-11 years at 13 days or less since completion of vaccination, which reduced to 1.1 (VE = 12%) 28 to 34 days after the end of vaccination.


Overall, the authors observed a rapid decline in LE for the 5-11 year age group. A similar reduction was observed for children aged 12 to 17, but the decrease was less pronounced than the younger cohort. Additionally, younger children had a substantial loss of protection one month after full immunization.

The marked reduction in VE in 11 year olds compared to 12 year olds could be attributed to the lower vaccine dose (10 µg) in the 5-11 year age group. Therefore, an appropriate number of vaccine doses and the quantity per dose should be optimized for best protection.

The authors could not include confirmed COVID-19 infections in residences because they are not reported. Home testing increased over the study period due to the Omicron surge, affecting observed estimates.

The study results support the protection conferred by vaccination against severe COVID-19 in young children, although the observation of a rapid loss of protection against infection marked by the appearance of the variant SARS-CoV-2 Omicron.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice/health-related behaviors, or treated as established information.

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