Covid-19 and the next outbreak: decreasing frailty by using mild stress?

The coronavirus disease 2019 (Covid-19) has resulted in many deaths, particularly of very old or obese people. These people are at risk to die in the event of an outbreak, like under one-year old babies were at risk to die one century ago from various diseases. It is argued that mild stress could help people to resist new outbreaks. The people who are obese because of bad feeding habits (snacking, junk food, overfeeding) and inactivity should adopt more healthy behaviours. Because an inactive way of life at old age can increase frailty, physical and mental activities should be kept at the highest possible level in elderly people, particularly if they live in retirement homes. In the event of an outbreak, management staff of these homes should not confine residents in their room for weeks or months, as it can increase inactivity, under-nutrition, sarcopenia, and depressive symptoms. People with or without co-morbidities should be active and one could wonder whether other mild stresses such as sauna bathing could help to better resist infection.