Estimating the impact of the COVID-19 vaccination programme in Ireland: December 2021-March 2023

Abstract Background In Autumn 2023, COVID-19 booster vaccines were offered to all those aged ≥50 years in Ireland. There was concern that vaccine fatigue would impact uptake. We aimed to quantify the direct impact of the COVID-19 vaccination programme on averted outcomes in individuals aged ≥50 years, during a period of Omicron variant dominance, to inform vaccination strategy and public health communication. Methods We conducted a retrospective observational study from December 2021 to March 2023 in Ireland. We considered as averted outcomes symptomatic SARS-CoV-2 presentations to primary care, emergency department (ED) presentations, hospitalisations, intensive care unit (ICU) admissions and deaths due to COVID-19. We used an adapted formula from other vaccine impact published studies, including national data on notified outcomes, vaccine coverage data and vaccine effectiveness (VE) estimates, sourced from the WHO’s live systematic VE review, to estimate the count and prevented fraction of outcomes in ≥ 50-year-olds averted by the COVID-19 vaccination programme. The number of expected outcomes in the absence of vaccination was calculated by summing the counts of outcomes observed and outcomes averted. Results Between December 2021 and March 2023, the COVID-19 vaccination programme averted 48,551 symptomatic presentations to primary care (36% of expected), 9,517 ED presentations (53% of expected), 102,160 hospitalisations (81% of expected), 3,303 ICU admissions (89% of expected) and 15,985 deaths (87% of expected). Conclusions During Omicron dominance, the COVID-19 vaccination programme averted symptomatic and severe outcomes, including deaths due to COVID-19, underscoring the benefits of COVID-19 vaccination. In the context of vaccine fatigue emerging as an important public health issue in Ireland and internationally, these findings can inform future COVID-19 booster vaccination programmes and communication about the reason for and importance of COVID-19 vaccination. Key messages • The COVID-19 vaccination programme in Ireland prevented illness and death in people aged ≥50-years. Vaccination therefore protected population health and the healthcare system. • These findings can be used to inform future COVID-19 vaccination policies, planning for winter, pandemic preparedness and communisation about the importance of ongoing COVID-19 vaccination programmes.