Abstract
Age is among the most prominent risk factors for developing severe COVID-19 disease, and therefore older adults are a major target group for vaccination against SARS-CoV-2. This review focusses on age-associated aspects of COVID-19 vaccines and vaccination strategies, and summarizes data on immunogenicity, efficacy and effectiveness of the four COVID-19 vaccines, which are licensed in the US and/or Europe; namely, the two mRNA vaccines by BioNTech/Pfizer (BNT162b2) and Moderna (mRNA-1273), and the adenovector vaccines developed by AstraZeneca/University Oxford (ChAdOx1-nCoV-19, AZD1222) and Janssen/Johnson&Johnson (Ad26.COV2-S), respectively. After very high protection rates in the first months after vaccination even in the older population, effectiveness of the vaccines, particularly against asymptomatic infection and mild disease, declined at later time points and with the emergence of virus variants. Many high-income countries have recently started administration of additional doses to older adults and other high-risk groups, whereas other parts of the world are still struggling to acquire and distribute vaccines for primary vaccination. Other vaccines are available in other countries and clinical development for more vaccine candidates is ongoing, but a complete overview of COVID-19 vaccine development is beyond the scope of this article.
Highlights
The immune system undergoes characteristic changes with age, which lead to dysregulation and functional deficits of many immune mechanisms
In the US, a third dose is recommended for persons with risk factors including adults older than 65 years 6 months after the second dose of an mRNA vaccine, and for all adults 2 months after a single dose of Ad26.COV2-S [83]
The unprecedentedly fast development of efficient vaccines against SARS-CoV-2 has prevented a large number of deaths and severe cases of disease over the last year, in older adults, and has helped to curtail viral spread in many countries
Summary
The immune system undergoes characteristic changes with age, which lead to dysregulation and functional deficits of many immune mechanisms. Additional risk factors for infections include chronic comorbidities, such as cardiovascular disease, kidney disease, diabetes or malignancies, which are frequent in the older population, and obesity, as well as immunosuppressive treatments, e.g., in the context of organ transplantation, chemotherapy or immunomodulatory treatment of autoimmune disease These phenomena have been observed and studied (e.g., for influenza, pneumococcal disease, and herpes zoster) for a long time [14,15,16]. Identification of risk factors is crucial for mitigation strategies, and a plethora of studies addressed these questions early in the pandemic They found that the risk for severe disease and death from COVID-19 is highest in older adults, persons with underlying co-morbidities, and obese individuals [20,21,22,23]. An overview of COVID-19 vaccines in children and adolescents has recently been published [30]
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