Asthma, diabetes, obesity, and learning difficulties are not self inflicted Sheikh
Wrt Obesity and type 2 diabetes. Lifestyle is very often not a choice. And it's just one of several causes of type 2 diabetes. There is, for example, also a strong genetic element for some people.
A major contributory factor for obesity and, separately type 2 diabetes, is stress. Stress causes inflammation. Which leads me to 'lifestyle'...
Lifestyle: - Poverty, mental ill health, physical health conditions including reduced mobility and/or pain, homelessness and housing insecurity (incidentally for those concerned about school closures, poor housing impacts heavily on a child's life chances).
As for definition of vulnerable. It depends what you're looking at, and there's a difference between risk of catching it and risk of dying from it. Globally the conditions with the very highest Covid death rates after dementia include cardiac issues, diabetes, and Down's Syndrome.
FYI, Down's and other learning disabilities, asthma too, are not self inflicted.