Pfizer's COVID vaccine is 56 percent less effective for a very young age group

Period of the study

One of the most important reasons why the findings of the study need to be carefully looked into is its timing. It was conducted between December 13 and January 30, simultaneous to the period of the recent spike in infections in the U.S.

It also involved 1.2 million children between the ages of 5-17 who have been vaccinated in the U.S. As per regulatory approvals sought by Pfizer, children between the ages of 5-11 have been given a pediatric dose consisting of 10 milligrams of the vaccine whereas adolescents between the age of 12 and 17 have been administered the regular adult dose of 30 milligrams. 

The researchers calculated the effectiveness of the vaccines administered to these age groups using the incidence rates of infection in the region and the comparing outcomes by vaccination status. 

Drop-in vaccine protection in younger children

The researchers found that the vaccine effectiveness dropped from 68 percent to just 12 percent in children aged between 5 and 11. Towards the end of the study period, the effectiveness dropped further in this age group to 11 percent. 

Vaccine effectiveness against hospitalization also dropped from 100 percent to 48 percent in this age group during this time. This was seen in children who were fully vaccinated. 

In comparison, adolescents who received a larger dose maintained their protection levels as vaccine effectiveness dipped from 66 percent to 51 percent while that against hospitalization dropped from 85 percent to 73 percent during the same period. 

The researchers state that the vaccine is still effective against severe disease and recommend its usage in children. They also suggest revising the dosage administered for this age group while continuing to rely on protections offered by other strategies such as wearing masks.

The study has not been peer-reviewed and was published on MedRxiv. 

Abstract:
Importance: There is limited evidence on the effectiveness of the BNT162b2 vaccine for children, particularly those 5-11 years and after the Omicron variant's emergence. Objective: To estimate BNT162b2 vaccine effectiveness against COVID cases and hospitalizations among children 5-11 years and 12-17 years during December 2021 and January 2022. Design: Analyses of cohorts constructed from linked statewide immunization, laboratory testing, and hospitalization databases. Setting/Participants: New York State children 5-17 years. Main outcomes/measures: New laboratory-confirmed COVID-19 cases and hospitalizations. Comparisons were made using the incidence rate ratio (IRR), comparing outcomes by vaccination status, and estimated vaccine effectiveness (VE: 1-[1/IRR]). Results: From December 13, 2021 to January 30, 2022, among 852,384 fully-vaccinated children 12-17 years and 365,502 children 5-11 years, VE against cases declined from 66% (95% CI: 64%, 67%) to 51% (95% CI: 48%, 54%) for those 12-17 years and from 68% (95% CI: 63%, 72%) to 12% (95% CI: 6%, 16%) for those 5-11 years. During the January 24-30 week, VE for children 11 years was 11% (95%CI -3%, 23%) and for those age 12 was 67% (95% CI: 62%, 71%). VE against hospitalization declined changed from 85% (95% CI: 63%, 95%) to 73% (95% CI: 53%, 87%) for children 12-17 years, and from 100% (95% CI: -189%, 100%) to 48% (95% CI: -12%, 75%) for those 5-11 years. Among children newly fully-vaccinated December 13, 2021 to January 2, 2022, VE against cases within two weeks of full vaccination for children 12-17 years was 76% (95% CI: 71%, 81%) and by 28-34 days it was 56% (95% CI: 43%, 63%). For children 5-11, VE against cases declined from 65% (95% CI: 62%, 68%) to 12% (95% CI: 8%, 16%) by 28-34 days. Conclusions and Relevance: In the Omicron era, the effectiveness against cases of BNT162b2 declined rapidly for children, particularly those 5-11 years. However, vaccination of children 5-11 years was protective against severe disease and is recommended. These results highlight the potential need to study alternative vaccine dosing for children and the continued importance layered protections, including mask wearing, to prevent infection and transmission.