Is it safe to run when you have pneumonia?

Rest is better: If there's a bear chasing you, then it's a good idea. Otherwise, you should rest.

Fine but not advised: It's technically OK to run while under treatment for pneumonia, but you may notice it's harder to run as the infection takes up space in the lung that is usually required for oxygen exchange. So you'd get winded more easily. But, with an infection as strong as a pneumonia, it's probably better to rest. Take a week off or so.