Measuring the impact of COVID-19 vaccination and immunity waning: A modelling study for Portugal

• Published in: Vaccine Vol. 40; no. 49; pp. 7115 - 7121
• Main Authors: Caetano, Constantino, Morgado, Maria Luísa, Patrício, Paula, Leite, Andreia, Machado, Ausenda, Torres, André, Pereira, João Freitas, Namorado, Sónia, Sottomayor, Ana, Peralta-Santos, André, Nunes, Baltazar
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 22.11.2022; Elsevier Limited; The Author(s). Published by Elsevier Ltd
• Subjects: Age groups; Aged; Asymptomatic; Child, Preschool; Compartmental models; Coronaviruses; COVID-19; COVID-19 - prevention & control; COVID-19 Vaccines; Disease control; Disease spread; Disease transmission; Effectiveness; Epidemiology; Hospitalization; Humans; Immunity; Infections; Intensive care; Modelling; Older people; Pandemics; Population; Portugal - epidemiology; Public health; SEIR model; Severe acute respiratory syndrome coronavirus 2; Vaccination; Vaccination Coverage; Vaccine effectiveness waning; Vaccine efficacy; Vaccines; Portugal; COVID-19; SEIR model; Compartmental models; Epidemiology; Vaccination; Vaccine effectiveness waning
• ISSN: 0264-410X; 1873-2518; 1873-2518
• DOI: 10.1016/j.vaccine.2022.10.007

Vaccination strategies to control COVID-19 have been ongoing worldwide since the end of 2020. Understanding their possible effect is key to prevent future disease spread. Using a modelling approach, this study intends to measure the impact of the COVID-19 Portuguese vaccination strategy on the effective reproduction number and explore three scenarios for vaccine effectiveness waning. Namely, the no-immunity-loss, 1-year and 3-years of immunity duration scenarios. We adapted an age-structured SEIR deterministic model and used Portuguese hospitalisation data for the model calibration. Results show that, although the Portuguese vaccination plan had a substantial impact in reducing overall transmission, it might not be sufficient to control disease spread. A significant vaccination coverage of those above 5 years old, a vaccine effectiveness against disease of at least 80% and softer non-pharmaceutical interventions (NPIs), such as mask usage and social distancing, would be necessary to control disease spread in the worst scenario considered. The immunity duration scenario of 1-year displays a resurgence of COVID-19 hospitalisations by the end of 2021, the same is observed in 3-year scenario although with a lower magnitude. The no-immunity-loss scenario presents a low increase in hospitalisations. In both the 1-year and 3-year scenarios, a vaccination boost of those above 65 years old would result in a 53% and 38% peak reduction of non-ICU hospitalisations, respectively. These results suggest that NPIs should not be fully phased-out but instead be combined with a fast booster vaccination strategy to reduce healthcare burden.