Vaccine effectiveness and duration of protection against symptomatic infections and severe Covid-19 outcomes in adults aged 50 years and over, France, January to mid-December 2021
Open accessAbstract
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. 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. 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. 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.
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Castillo and colleagues noted that waning of protection following infection with Delta was less pronounced against COVID-19 related hospitalizations than against symptomatic infection.
“Moreover, as observed in this study, Castillo and colleagues noted that waning of protection following infection with Delta was less pronounced against COVID-19 related hospitalizations than against symptomatic infection [12].”
From Vaccine effectiveness and duration of protection of COVID-19 mRNA vaccines against Delta and Omicron BA.1 symptomatic and severe COVID-19 outcomes in adults aged 50 years and over in France (2023) · cites this paper as [12]
The Results (‘Vaccine effectiveness against different variants’) report that protection against symptomatic Delta infection decreased over time, while protection against hospitalization did not appear to decrease in the first three months. This supports the comparison, but the paper studies waning protection after vaccination, not protection following a Delta infection. (LLM, conf=0.82)
Experimental — accuracy not yet measuredThe decrease in protection was substantially higher against Omicron BA.1 compared to Delta.
“this decrease in protection was substantially higher against Omicron BA.1 compared to Delta [3,8,12,19,26].”
From Vaccine effectiveness and duration of protection of COVID-19 mRNA vaccines against Delta and Omicron BA.1 symptomatic and severe COVID-19 outcomes in adults aged 50 years and over in France (2023) · cites this paper as [12]
The Discussion (page not supplied) says vaccine effectiveness was only slightly lower against Delta than against earlier variants, while preliminary estimates pointed to very little or no protection against symptomatic Omicron infection. This supports the general contrast, but the paper does not identify BA.1 or measure a substantially greater decrease against BA.1 than against Delta; its analyses preceded Omicron’s rapid spread in France. (LLM, conf=0.82)
Experimental — accuracy not yet measuredOnly a few studies have reported on vaccine protection in the French population, especially among those most at risk of severe COVID-19 disease.
“To date, only a few studies [12,23,24] have reported on the protection afforded by vaccines in the French population, especially among the most at risk of severe COVID-19 disease.”
Additional vaccine effectiveness studies revealed waning of vaccine-induced protection over time.
“However, as vaccination campaigns progressed, additional vaccine effectiveness (VE) studies revealed waning of the vaccine-induced protection over time [8-13]”
Several studies have described a drop over time of two-dose vaccine effectiveness against SARS-CoV-2 symptomatic infection.
“Several studies have described a drop over time of two-dose vaccine effectiveness against SARS-CoV-2 symptomatic infection;”
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Evaluation of Waning of SARS-CoV-2 Vaccine–Induced Immunity: A Systematic Review and Meta-analysis
Menegale, F., Manica, M., Zardini, A., Guzzetta, G., Marziano, V., d'Andrea, V., Trentini, F., Ajelli, M., Poletti, P., & Merler, S. (2023) · JAMA Network Open · doi:10.1001/jamanetworkopen.2023.10650 · Cited by 280 · see citing works
Tamandjou Tchuem, C. R., Auvigne, V., Vaux, S., Montagnat, C., Paireau, J., Monnier Besnard, S., Gabet, A., Benhajkassen, N., Le Strat, Y., Parent Du Chatelet, I., et al. (2023) · Vaccine · doi:10.1016/j.vaccine.2023.02.062 · Cited by 27 · see citing works
- Authors
- Suarez Castillo, M., Khaoua, H., & Courtejoie, N.
- Affiliations
- Ministère des Solidarités et de la Santé (FR)
- ORCID
- Courtejoie, Noémie
- Venue
- Global Epidemiology
- Publisher
- Elsevier BV
- Published
- 2022-12
- Volume
- 4
- Pages
- 100076
- ISSN
- 2590-1133 (ISSN-L)
- PMC
- PMC9135646
- OpenAlex
- W4281682639
- Cited by
- 13
- References
- 3
- Citations by year
- 2026: 1 · 2025: 1 · 2024: 4 · 2023: 6 · 2022: 1
- FWCI
- 1.47
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- Locations
- Global Epidemiology (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- Funders
- DREES
- Topics
- Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
- Social Sciences › Health › Vaccine Coverage and Hesitancy
- Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
- Keywords
- COVID-19 vaccines, vaccine effectiveness, waning immunity, duration of protection, older adults, symptomatic infection, hospitalization, intensive care unit admission, inpatient deaths, booster vaccination, SARS-CoV-2 variants, Delta variant, test-negative case-control design, survival analysis
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