Abstract
Background
SARS-CoV-2 continues to spread despite fast vaccine rollout, which could be attributed to waning immunity or to a reduced protection against some variants. A thorough characterization of vaccine protection and its duration in time is needed to inform vaccination policies and enhance public trust.
Methods
We linked three national databases with exhaustive information on screening, vaccination and hospitalizations in France from January 1st to December 12, 2021. We performed a two-step analysis to estimate vaccine effectiveness against severe outcomes of Covid-19 (requiring hospitalization) in people aged 50 years or over, combining: (i) a test-negative case–control design to assess vaccine effectiveness against symptomatic infections; and (ii) a survival analysis to assess the additional protection against severe outcomes (hospitalizations, ICU admissions and inpatient deaths) in infected individuals.
Findings
We found a high vaccine effectiveness in people aged 50 years or more, reaching 82% against symptomatic infections and 94% against hospitalizations, after a full vaccination scheme with the Covid-19 vaccines used in France.
Vaccine effectiveness against symptomatic infections decreased over time, dropping to 53% after six months, but remained high against severe outcomes (90% after six months). The booster dose allowed restoring protection levels above 90% against symptomatic infections. Vaccine protection and its evolution in time, showed little difference against the variants that circulated prior to December 2021 in France, including the Delta variant.
Interpretation
Though vaccine immunity decreases over time, vaccination remains crucial to provide individual protection against severe outcomes requiring hospitalization. This decline can be reversed by the receipt of a booster dose.
【저자키워드】 COVID-19, SARS-CoV-2, Vaccine, Effectiveness, booster, test-negative design, Real-world estimates, 【초록키워드】 Evolution, vaccination, Hospitalization, variant, outcome, delta variant, database, variants, Spread, survival, symptomatic, hospitalizations, ICU admission, France, information, booster dose, symptomatic infection, Analysis, deaths, waning immunity, infected individuals, finding, National, symptomatic infections, vaccine immunity, decrease, ENhance, performed, remained, reduced, reversed, 【제목키워드】 outcome, France, symptomatic infection,