OK here is my experience. I'm 78. As you age your immune system gets weaker. Starting sometime in my early 60's I got a runny nose. This turned into or was the flu but not always. This often led to pneumonia and this was scary. I couldn't breath and thought my lungs were coming out of my throat. Then as often as not it turned into pneumonia and I would wonder am I going to make it this time or not. So I started to get a flu shot every year and the pneumonia shot ever 5 or 10 years, I forget how often it's required. For the last dozen years or so I haven't had a problem.
