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A recent report Published in December 2024 by the European Centre for Disease Prevention and Control (ECDC) presents the results of a comprehensive analysis of the effectiveness of the COVID-19 vaccine in eight countries Europeans. This study, based on electronic medical records, evaluates the impact of the monovalent dose of the Pfizer XBB.1.5 vaccine against disease-related hospitalizations and deaths.
Methodology and population studied
The analysis focused on people over 65 years of age living in Belgium, Denmark, Italy, the Netherlands, Norway, Portugal, Spain (Navarra) and Sweden. The population was divided into two groups. Some were over 80 years of age and others were in the range of 65 to 79 years.
The study period spanned from October 2023 to April 2024, using retrospective cohorts and monthly updated data. During this time, vaccine effectiveness (VE) was monitored in eight-week windows.
Main results
1. Initial vaccine protection
In the first eight weeks after the administration of the autumn dose (October-November 2023):
- Hospitalization for COVID-19:
- 65% (CI 95%: 56-71) in ?80 years.
- 64% (CI 95%: 55-72) in 65-79 years.
- COVID-19 related deaths:
- 67% (CI 95%: 41-81) in ?80 years.
- 67% (CI 95%: 43-81) in 65-79 years.
2. Reduction in effectiveness over time
From January 2024, effectiveness began to decline, probably due to the emergence of new SARS-CoV-2 variants and the time elapsed since vaccination:
- January-February 2024:
- Hospitalization: 38% (?80 years) and 48% (65-79 years).
- Deaths: 40% (?80 years) and 54% (65-79 years).
3. Variability in estimates
Between February and April 2024, the accuracy of estimates decreased significantly, making definitive conclusions difficult in some countries.
Key Observations
- People vaccinated with the fall dose had more vaccination histories and higher rates of comorbidities, which could influence the results.
- The decrease in effectiveness reflects not only biological factors, but also biases in the population studied.
The XBB.1.5 monovalent dose administered in the fall of 2023 was shown to be effective in reducing the risk of hospitalization and death from COVID-19 in older adults. However, its effectiveness declined significantly after three months, highlighting the need for continued strategies to protect the most vulnerable populations from the disease.
