COVID-19 Vaccine Effectiveness Against Omicron Infection and Hospitalization

Abstract

OBJECTIVES: This study aimed to provide real-world evidence on coronavirus disease 2019 vaccine effectiveness (VE) against symptomatic infection and severe outcomes caused by Omicron in children aged 5 to 11 years. METHODS: We used the test-negative study design and linked provincial databases to estimate BNT162b2 vaccine effectiveness against symptomatic infection and severe outcomes caused by Omicron in children aged 5 to 11 years between January 2 and August 27, 2022 in Ontario. We used multivariable logistic regression to estimate VE by time since the latest dose, compared with unvaccinated children, and we evaluated VE by dosing interval. RESULTS: We included 6284 test-positive cases and 8389 test-negative controls. VE against symptomatic infection declined from 24% (95% confidence interval [CI], 8% to 36%) 14 to 29 days after a first dose and 66% (95% CI, 60% to 71%) 7 to 29 days after 2 doses. VE was higher for children with dosing intervals of ≥56 days (57% [95% CI, 51% to 62%]) than 15 to 27 days (12% [95% CI, −11% to 30%]) and 28 to 41 days (38% [95% CI, 28% to 47%]), but appeared to wane over time for all dosing interval groups. VE against severe outcomes was 94% (95% CI, 57% to 99%) 7 to 29 days after 2 doses and declined to 57% (95%CI, −20% to 85%) after ≥120 days. CONCLUSIONS: In children aged 5 to 11 years, 2 doses of BNT162b2 provide moderate protection against symptomatic Omicron infection within 4 months of vaccination and good protection against severe outcomes. Protection wanes more rapidly for infection than severe outcomes. Overall, longer dosing intervals confer higher protection against symptomatic infection, however protection decreases and becomes similar to shorter dosing interval starting 90 days after vaccination.

Infection‐induced seroconversion and seroprevalence of SARS‐CoV‐2 among a cohort of children and youth in Montreal, Canada

“…Older participants had a vaccine uptake exceeding 90%. Though older children may have been vaccinated over a year before their fourth round DBS, and BNT162b2 vaccine effectiveness against Omicron may wane significantly by 120 days, 12 approximately one third of the older children had a second, third or fourth dose within 120 days of their DBS. This finding was consistent with CDC data demonstrating greater increases in seroprevalence between September and February 2022 among age groups with the lowest vaccination rates 13 .…”

“Flying a plane and building it at the same time”: Lessons learned from the dynamic implementation of mass vaccination clinics in the Region of Waterloo, Ontario, Canada

“…On 11 March 2020, the World Health Organization declared COVID-19 a global pandemic [ 1 ], and less than 9 months later, on 9 December 2020, Health Canada approved the first vaccine for emergency use [ 2 ]. COVID-19 immunizations have since played a significant role in reducing the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on public health, despite its evolution, by minimizing hospitalizations [ 3 , 4 ], severe illness [ 5 – 7 ] and deaths [ 4 , 8 ]. However, going from vaccine approval to rapidly implementing mass vaccination clinics in Canada’s various provinces and regions also required an unprecedented collaboration among many stakeholders.…”