Posted on 20 July 2020
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The nature of COVID-19 as a disease that primarily affects the elderly poses a conundrum for the development of a vaccine: the fact that vaccination is generally less effective as we age.
“Up until very recently most of the focus of the vaccine community has been on saving lives of young children,” says Martin Friede, the World Health Organization’s coordinator for vaccine product and delivery research. “The people who need the vaccine the most may actually be the people in whom the vaccine might not work.”
This reduced effectiveness with age is caused by the decline of the immune system, in particular the decline of an organ called the thymus, in which T cells are ‘trained’ to recognise pathogens.
Firstly, aging depletes the arsenal of adaptable T-cells, as the thymus fills with fatty tissue. As a result, our immune systems become ill-equipped to fight off new viruses. […] Second, the aging thymus may also complicate vaccine development for the pandemic. Vaccines provide instructions for our immune system, which T-cells help pass along. By age 40 or 50, the thymus has exhausted most of its reserve of the kind of T-cells that can learn to recognize unfamiliar pathogens—and ‘train’ other immune cells to fight them. Many vaccines rely on such T-cells.
Consequently, researchers are having to pay closer attention to the effects of vaccines on older individuals, and must find ways to improve their response to immunisation. These include increasing the amount of antigen (the molecule by which the immune system recognises the pathogen) contained by the vaccine, or using adjuvants – added ingredients that make the immune system respond more strongly to the vaccine, which leads to better immune memory.