Review of the background to increased risks of SARS-CoV-2 pneumonia among elderly people

Morbidity and mortality rates during the COVID-19 pandemic have been particularly high among elderly people (>65 years). This review summarises some of the important physiological and clinical aspects in the background of augmented risk. Airway clearance provides defence against inhaled particles, including viruses. Some relevant studies have indicated that clearance from the small and large airways is slower in elderly people. Cough peak flow (the speed of expiratory airflow during coughing, or cough power) is another important parameter that reflects the defence capacity of the respiratory system. Age has likewise been shown to induce inspiratory and expiratory muscle weakness and, as a consequence, a low cough peak flow. In addition to the weakening of these non-specific defences in elderly people, the specific immune response against the SARS-CoV-2 virus has been found to be nearly blocked in aged mice, and the augmented synthesis of prostaglandin D2 (PGD2) was found to play a role in this phenomenon. Aged animals were protected from death by a specific antagonist of PGD2. Among aged people suffering from COVID-19, there were disproportionally more patients with low CD8 T lymphocyte counts and high plasma concentrations of interleukin 6 (IL-6). This combination of deficient cellular immunity and overt inflammatory response in COVID-19 has been identified as a significant risk factor of mortality.