Efficacy and Safety of COVID-19 Vaccines in Older People

Roy L. Soiza; Chiara Scicluna; Emma C. Thomson


Age Ageing. 2021;50(2):279-283. 

In This Article

mRNA Vaccines

Two of the vaccines reporting the earliest Phase III results, manufactured by Pfizer and Moderna, are novel messenger RNA (mRNA) vaccines. Both reported initial results suggesting efficacies in excess of 90%. They work by injecting mRNA encoding the SARS-CoV-2 spike protein directly into the host. Although pure mRNA is rapidly downgraded, a number of technological advances in delivery methods and RNA carriers over the last decade allow efficient and safe uptake of mRNA into the cytosol, where ribosomes then translate the mRNA to produce a viable protein that can then stimulate an immune response. This technology has a number of theoretical advantages over more conventional vaccine types, including improved safety (as no infectious agents are involved in their production), low potential for mutations, lower risk of antigen degradation in vivo, and the potential for rapid mass production at lower cost, as in vitro reactions can rapidly generate high yields of the therapeutic agent.[3] However, little is known about the efficacy and safety of mRNA vaccines in older people, especially at the extremes of old age and in those with frailty. A phase I study of the Moderna vaccine in 'older adults' published in the New England Journal of Medicine received considerable media attention after it found antibody responses were similar to those seen in younger people.[4] However, this study included only 40 healthy people aged 58 or over, so its relevance to older people with frailty is unclear. Self-limiting mild to moderate adverse events were common, with all 20 participants aged 71 or over (mean age 72.6y) reporting local side effects such as pain at the injection site and 80% reporting systemic symptoms such as lethargy. Over 25% (around 8,000) participants of the Moderna phase III study are aged 65 or over and a similar proportion have chronic diseases, so the evidence base will improve once full interim results are published. For the Pfizer vaccine, published data on older participants are even more sparse. However, a press release from Pfizer claimed over 95% efficacy in their over-65 age group (but with no supporting details or figures)[5] and over 40% of participants in their Phase III trial are aged between 56 and 84.