Effectiveness of Pfizer-BioNTech COVID-19 vaccine in children and teens declines over time

March 4, 2022

Two doses of the Pfizer-BioNTech vaccine protect children and adolescents against COVID-19-associated emergency department (ED) and urgent care (UC) encounters. However, vaccine effectiveness (VE) was lower during Omicron predominance and decreased with time since vaccination, the Centers for Disease Control and Prevention (CDC) reported in its Morbidity and Mortality Weekly Report (MMWR).

The CDC said the study provides updated real-world data on the effectiveness of the vaccine in this younger age group, particularly against the Omicron variant of SARS-CoV-2 and on the duration of protection.

The study analyzed 39,217 emergency department and urgent care encounters and 1,699 hospitalizations with COVID-19-like illness among non-immunocompromised patients aged 5-17 years with COVID-19-like illness. The 10-state data covered the timeframe of April 9, 2021-January 29, 2022.

Among adolescents aged 12-17 years during the full study period — including pre-Delta, Delta, and Omicron predominant periods — 2-dose estimates of vaccine effectiveness were higher (76%-83%) 14-149 days after receipt of a second dose, and significantly lower (38%-46%) at 150 days or longer post-vaccination. However, a third vaccine dose restored vaccine effectiveness against COVID-19-associated emergency department or urgent care center encounters to 86% among adolescents aged 16-17 years.

Among children aged 5-11 years during the full study period, vaccine effectiveness of two doses (14-67 days earlier) against COVID-19-associated ED or UC encounters was 46%, which was significantly lower than overall estimates for adolescents aged 12-17 years.

However, most encounters among children aged 5-11 years occurred during Omicron predominance, when VE significantly declined for adolescents aged 12-17 years. During Omicron predominance, VE of a second dose received 14-149 days earlier was 45% and 34% for adolescents aged 12-15 and 16-17 years, respectively, suggesting that the lower VE observed among children aged 5-11 years was likely driven by the predominant variant rather than differences in VE across age groups.

During Omicron predominance, there was no evidence of protection for adolescents aged 12-17 years from 2 doses received 150 days or longer; however, a third vaccine restored VE to 81% among adolescents aged 16–17 years.

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