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

Constantino Caetano, Maria Luísa Morgado, Paula Patrício, Andreia Leite, Ausenda Machado, André Torres, João Freitas Pereira, Sónia Namorado, Ana Sottomayor, André Peralta-Santos, Baltazar Nunes

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)
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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.

Original languageEnglish
Pages (from-to)7115-7121
Number of pages7
Issue number49
Publication statusPublished - 22 Nov 2022


  • Compartmental models
  • COVID-19
  • Epidemiology
  • SEIR model
  • Vaccination
  • Vaccine effectiveness waning


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