Evaluating the impact of COVID-19 vaccination strategies on infections and hospitalisations in Victoria with non-seasonal epidemic wave patterns: a modelling study.

Abstract

To assess the impact of different coronavirus disease 2019 (COVID-19) vaccination strategies on infections and hospitalisations in the context of non-seasonal epidemic waves. Dynamic compartmental model-based analysis. Victoria (Australia). Alternative COVID-19 vaccination strategies: baseline (low population coverage - 18-64 years, 7%; 65 years or older, 44% - vaccinations distributed evenly across the year); high coverage for all age groups, with vaccinations spread across year; increased coverage for people aged 65 years or older; annual vaccination campaigns that achieve coverage equivalent to that of influenza vaccinations (18-64 years, 25%; 65 years or older, 59%), commencing in March (same time as influenza vaccination campaign), August, or December; no further COVID-19 vaccinations for people under 65 years of age; no further COVID-19 vaccinations for anyone. Vaccination scenarios used different assumptions about COVID-19 epidemic wave periodicity, and peak infections magnitude and month. Mean incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections and COVID-19-related hospitalisations over a ten-year projection period. The low baseline population level of recent COVID-19 vaccination means that any increase in coverage could reduce infection and hospitalisation incidence. Increasing COVID-19 vaccination coverage to match that of influenza vaccination with an annual vaccination campaign reduced the mean incidence of infections by 1-13% and that of hospitalisations by 3-14%, depending on the timing of vaccination campaigns with respect to the epidemic infections peak and assumptions about epidemic wave characteristics. Increasing coverage for people aged 65 years or older reduced hospitalisation incidence by 9-26%, but required twice as many vaccine doses as the annual campaign strategies. Annual COVID-19 vaccination campaigns at the same time as those for influenza vaccination could reduce the number of COVID-19-related hospitalisations, with lower logistical requirements than alternative approaches.