COVID-19 Vaccine Effectiveness Against Omicron Infection and Hospitalization

Area of Science:

• Immunology
• Public Health
• Pediatrics

Background:

• The Omicron variant of SARS-CoV-2 poses a significant threat to public health.
• Vaccine effectiveness (VE) data for pediatric populations against Omicron are crucial for guiding vaccination strategies.
• Real-world evidence is needed to assess the BNT162b2 vaccine's performance in children aged 5 to 11 years.

Purpose of the Study:

• To provide real-world evidence on the effectiveness of the BNT162b2 vaccine against symptomatic infection and severe outcomes caused by the Omicron variant in children aged 5 to 11 years.
• To evaluate the impact of dosing intervals and time since vaccination on vaccine effectiveness.
• To inform public health recommendations for pediatric COVID-19 vaccination.

Main Methods:

• A test-negative study design was employed using linked provincial databases in Ontario.
• Multivariable logistic regression was used to estimate VE against symptomatic infection and severe outcomes.
• Data were collected between January 2 and August 27, 2022, including 6284 test-positive cases and 8389 test-negative controls.

Main Results:

• VE against symptomatic Omicron infection was 24% after one dose and 66% after two doses (7-29 days post-vaccination).
• VE against symptomatic infection was higher with longer dosing intervals (≥56 days: 57%) compared to shorter intervals (15-27 days: 12%).
• VE against severe outcomes was 94% within 7-29 days after two doses, waning to 57% after ≥120 days.

Conclusions:

• Two doses of BNT162b2 provide moderate protection against symptomatic Omicron infection and good protection against severe outcomes in children aged 5 to 11 years.
• Protection against infection wanes more rapidly than protection against severe outcomes.
• Longer dosing intervals enhance initial protection against symptomatic infection, but this advantage decreases over time.