According to the current state of studies, the question of the duration of vaccination protection cannot be answered in a blanket manner, but varies depending on vulnerability characteristics such as age and previous illnesses.
In the pivotal study population of Comirnaty® (BionTech/Pfizer), efficacy against severe illness and hospitalization with SARS-CoV-2 alpha 6 months after dose 2 remains very high at 95.7% (95% CI: 73.9-99.9), as shown by follow-up analyses [1]. Vaccination was still very effective in preventing symptomatic alpha infections 6 months after dose 2 in the population studied, at 84% (12% less compared with time point 2 months) [1].
Booster vaccination for those at particular risk ?
Protection against PCR-positive delta infections also reduces over time, as shown by data from Israel and the United Kingdom [2,3,6]. However, based on the data known to date from observational studies of the delta variant conducted in a period up to a maximum of 7 months after dose 2, there is no evidence that there was a significant decrease in efficacy against severe disease and hospitalization with delta compared with alpha during this period [3]. However, it can be assumed that the vaccination protection against mild diseases with the delta variant lasts less long than against the alpha variant. Thus, infections may occur more frequently before 12 months after vaccination compared to the alpha variant, especially in older age groups.
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The Swiss National Covid-19 Science Taskforce recommends determination of SARS-CoV-2 anti-spike immunoglobulin G (IgG) levels in immunodeficient individuals four weeks after the 2nd mRNA vaccine dose [8]. If these antibody titers are within four weeks of the 2. vaccination in the clear positive range defined for the respective test assay applied, is referred to a 3rd vaccination waived. However, when such antibodies are not detectable in the clear positive range or are absent, current scientific data indicate that vaccination response can be improved by a third vaccination. |
Risk of reinfection higher among over 60-year-olds
Modeling analyses based on antibody history indicate that protection against infection is 3 years or more for severe disease in fully vaccinated persons <65 years, whereas mild infections (with virus transmission) can occur from 16 months. For >65-year-old individuals, protection from infection is expected to be shorter: in the range of 8-10 months for mild disease and 15-24 months for severe disease [4].
Observational studies show that re-infection with SARS-CoV-2 is rare up to 12 months after infection, but may occur after a shorter interval with increasing age [5]. The risk of becoming infected with SARS-CoV-2 delta increases significantly in all adult age groups if the 2nd Comirnaty vaccination dose was given more than 146 days ago [2], especially in persons 60 years of age and older (odds ratio 3 [95% CI, 1.85-5.12]). The question of the duration of vaccination protection in relation to 70- to 97-year-olds is currently being investigated in Germany in a study conducted by the Charité in cooperation with a Berlin family practice study [7].
Literature:
- Thomas SJ, et al: medRxiv 2021.07.28.21261159.
- Israel A, et al: medRxiv preprint doi: https://doi.org/10.1101/2021.08.03.21261496
- Swiss National Covid-19 Science Taskforce, 8/26/21, https://sciencetaskforce.ch, (last accessed 09/05/21).
- Khoury DS, et al: Nature medicine 2021. 10.1038/s41591-021-01377-8.
- Hansen CH, et al: Lancet (London, England) 2021; 397(10280): 1204-1212.
- Pouwels KB: Impact of Delta on viral burden and vaccine effectiveness against new SARS-CoV-2 infections in the UK, www.ndm.ox.ac.uk/files/coronavirus (last accessed Sept. 05, 2021).
- “Charité study demonstrates delayed vaccination response in the elderly Charité press release,” Charité Universitätsmedizin Berlin, June 09, 2021.
- Swiss National Covid-19 Science Taskforce, 8/26/21, https://sciencetaskforce.ch, (last accessed 09/05/21).
HAUSARZT PRAXIS 2021; 16(9): 18 (published 9/19-21, ahead of print).
