Projecting the impact of a two-dose COVID-19 vaccination campaign in Ontario, Canada

Thomas N Vilches; Kevin Zhang; Robert Van Exan; Joanne M Langley; Seyed M Moghadas

doi:10.1016/j.vaccine.2021.03.058

Projecting the impact of a two-dose COVID-19 vaccination campaign in Ontario, Canada

Vaccine. 2021 Apr 22;39(17):2360-2365. doi: 10.1016/j.vaccine.2021.03.058. Epub 2021 Mar 20.

Authors

Thomas N Vilches¹, Kevin Zhang², Robert Van Exan³, Joanne M Langley⁴, Seyed M Moghadas⁵

Affiliations

¹ Institute of Mathematics, Statistics and Scientific Computing, University of Campinas, Campinas, SP, Brazil.
² Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8 Canada. Electronic address: kevink.zhang@mail.utoronto.ca.
³ Immunization Policy & Knowledge Translation, Trent Lakes, Ontario K0M 1A0, Canada.
⁴ Canadian Center for Vaccinology, Dalhousie University, IWK Health Centre and Nova Scotia Health Authority, Halifax, Nova Scotia B3K 6R8 Canada.
⁵ Agent-Based Modelling Laboratory, York University, Toronto, Ontario M3J 1P3 Canada.

Abstract

Background: A number of highly effective COVID-19 vaccines have been developed and approved for mass vaccination. We evaluated the impact of vaccination on COVID-19 outbreak and disease outcomes in Ontario, Canada.

Methods: We used an agent-based transmission model and parameterized it with COVID-19 characteristics, demographics of Ontario, and age-specific clinical outcomes. We implemented a two-dose vaccination program according to tested schedules in clinical trials for Pfizer-BioNTech and Moderna vaccines, prioritizing healthcare workers, individuals with comorbidities, and those aged 65 and older. Daily vaccination rate was parameterized based on vaccine administration data. Using estimates of vaccine efficacy, we projected the impact of vaccination on the overall attack rate, hospitalizations, and deaths. We further investigated the effect of increased daily contacts at different stages during vaccination campaigns on outbreak control.

Results: Maintaining non-pharmaceutical interventions (NPIs) with an average of 74% reduction in daily contacts, vaccination with Pfizer-BioNTech and Moderna vaccines was projected to reduce hospitalizations by 27.3% (95% CrI: 22.3% - 32.4%) and 27.0% (95% CrI: 21.9% - 32.6%), respectively, over a one-year time horizon. The largest benefits of vaccination were observed in preventing deaths with reductions of 31.5% (95% CrI: 22.5% - 39.7%) and 31.9% (95% CrI: 22.0% - 41.4%) for Pfizer-BioNTech and Moderna vaccines, respectively, compared to no vaccination. We found that an increase of only 10% in daily contacts at the end of lockdown, when vaccination coverage with only one dose was 6%, would trigger a surge in the outbreak. Early relaxation of population-wide measures could lead to a substantial increase in the number of infections, potentially reaching levels observed during the peak of the second wave in Ontario.

Conclusions: Vaccination can substantially mitigate ongoing COVID-19 outbreaks. Sustaining population-wide NPIs, to allow for a sufficient increase in population-level immunity through vaccination, is essential to prevent future outbreaks.

Keywords: COVID-19; Outbreak simulation; Vaccination.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Aged
COVID-19 Vaccines
COVID-19*
Communicable Disease Control
Humans
Ontario
SARS-CoV-2
Vaccination

Substances

COVID-19 Vaccines